INTRODUCTION Fat and oil are commonly used in poultry diets to increase the energy density as they yield 2.25 times more calories than carbohydrates and protein. Fat-supplemented diets increase the feed efficiency and profitability in poultry. Besides, oil improves the palatability of diets, reduces the dustiness of feeds and decreases the passage rate of feed through the intestinal tract of poultry, which gives more time for the adequate absorption of all nutrients present in the diet (Baião and Lara 2005). Poultry nutritionists invariably incorporates different sources of oil as an energy source to increase the palatability of feed, feed efficiency and for deposition of fat in broilers. The dietary supplementation vegetable oils alter the fatty acid profile of thigh and breast muscles broiler meat (Valavan et al., 2006; Abdulla et al. 2015) and dietary composition influences the nutritive quality of poultry meat. Rapeseed oil (Brassica napus var.) has been known as a good source of α-linolenic acid (ALA, C18:3 n-3), which can be readily converted to n-3 long chain polyunsaturated fatty acids (LC-PUFA) in poultry and can be included in vegetable oil blends along with sunflower oil, rice bran oil and palm oil to improve omega -3- fatty acid content of broiler ration (Valavan et al., 2006). Thus a study was proposed to find effects of replacing palm oil with rapeseed oil on growth performance in different stages of broiler chicken. MATERIALS AND METHOD Experimental details and data: This work was supported by the research grant of Kerala Veterinary and Animal Sciences University, Wayanad, Kerala, India. Experimental study was approved by Institutional animal ethical committee under 1271/GO/Re/S/09/CPCSEA- IAEC/COVAS/PKD/10/2019. The feeding experiment was conducted in Instructional Livestock Farm Complex, College of Veterinary and Animal Sciences, Kerala Veterinary and Animal Science University, Wayanad, Kerala from the period of January to February 2019. One hundred sixty, day-old Vencobb 400 broiler chicks were purchased from local hatchery and were separated into four groups (G1, G2, G3 and G4) with four replicates with ten chicks. The experimental rations was prepared as per BIS (IS: 1374; 2007) recommendations. The basal diets (R1) were prepared with vegetable oil (palm oil) included at the rate of 1.5, 3.0, and 4.5 per cent in pre-starter, starter and finisher ration, respectively. The treatment rations R2, R3 and R4 was prepared with rapeseed oil replacing 25, 50 and 100 per cent of palm oil included in R1, respectively. The ingredient composition of the experimental ration of broiler pre-starter, starter and finisher diet are presented in Table 1, 2 and 3. The feed was prepared at feed mill facilities in Instructional Livestock Farm Complex (ILFC). Feed and water were supplied ad libitum up to 42nd day of its age. Growth performance: Daily feed consumption was calculated by the amount of feed consumed by each bird by subtracting the leftover feed from total feed offered in a day. The live body weight of experimental birds were recorded at weekly intervals in morning hours after withdrawing feeders. Weight gain and body weight was calculated for all replicates from the data collected. Feed conversion ratio (FCR) was calculated by dividing the feed consumption by weight gain at different stage of growth. Statistical Analysis: The data obtained in this study were analyzed statistically as per the methods described by Snedecor and Cochran (1994) using the SPSS version 21.0 ® software. RESULT AND DISCUSSION A. Growth performance Growth performance of pre-starter, starter and finisher period of broiler is presented in Table 4. During the finisher period feed conversion ratio and weight gain was significantly (P<0.01) influenced due to dietary replacement of palm oil with rapeseed oil in the present study. Body weight gain during finisher period was significantly higher in G3 group (1490.55g) and G4 (1481.74g) compared to other groups and better feed conversion ratio (FCR) (P<0.01) was observed in G4 (100 per cent rapeseed oil) group and G3 (50 per cent rapeseed oil replaced group) in the basal diet. Feeding palm oil and rapeseed oil at different proportions does not affect feed intake of birds between treatment groups. Similar to our findings, Wang et al. (2013); Khatun et al. (2016) concluded in their study that weight gain and FCR was in increasing trend with the increased levels of sunflower oil replacing palm oil when included at 6 per cent in the broiler ration during the finisher period. The research findings of other researchers were compared with different oils like rapeseed oil, sunflower oil, soyabean oil and palm oil and their combinations at 5 per cent (Ghasemi et al., 2015); 6 per cent (Khatun et al., 2016; Baighi and Nobakht 2017) not affected the feed intake during grower and finisher periods in broilers (Abbasi et al., 2021). The improved feed conversion efficiency and weight gain might be due to ratio of saturated and unsaturated fatty acids present in broiler diets. The higher saturated and unsaturated fatty acid ratio in diet needs a higher concentration of bile salts and pancreatic lipase, which are essential for fat digestion and absorption which affect their growth (Burlikowska et al., 2010). Hence, rapeseed oil containing diet, which has a higher ratio of UFA and SFA which leads to better fat digestibility (Nobakht et al., 2012).