The present study aimed to investigate the effects of different digestible and metabolizable energy levels to protein ratio to obtain optimum ratio in rainbow trout (Oncorhynchus mykiss) diet. This experiment was carried out with 2600 (control), 2900, 3200, 3500 and 3800 kcal/kg digestible energy (DE) that equal to 2250, 2500, 2750, 3000 and 3300 kcal/kg metabolizable energy (ME) with 35 % protein (CP) in  the diet. The DE/CP ratios were 74, 83, 92, 100, 108 and for ME/CP; 64, 71, 78, 86 and 94, respectively. Five treatments were compared in a completely randomized design with 200 fish (average weight; 195 ± 5 g) with 4 replicates for 9 weeks. According to the results, the higher growth rate was observed, when the energy to protein ratio increased compared to control group. Fish fed DE/CP=100 (ME/CP=86) dietary content significantly showed the highest weight gain compared to other treatments and improved feed conversion ratio (FCR) and specific growth rate as well (p<0.05). In all treatments, no significant differences were observed for dry matter and ash content of flesh compared to control group (p>0.05). Moreover, fat content significantly increased, but protein content significantly decreased when DE/CP increased (p<0.05). Therefore, it is recommended that diet contains 35 % CP and 3500 or 3000 kcal/kg DE and ME, respectively (DE/CP = 100 and ME/CP = 86) at the finishing stage of rainbow trout is more effective.