This study was conducted to investigate the potential of milkweed seed powder (Calotropis procera) to be included in the diet of rainbow trout (Oncorhynchus mykiss) in five levels 1, 2, 3, 4 and 5 percent plus control (zero percent) in a completely randomized design triplicated. To perform the test, 3,600 rainbow trout fries (11.5±3.64 g) were distributed in 18 raceways. After two weeks of acclimatization, the fish were fed with six experimental diets for 56 days. Growth indices, hepatosomatic index, gastro somatic index, feed efficiency ratio as well as whole body chemical composition, survival and feed conversion ratio were studied. The results showed that an increase in milkweed seed powder up to 4%, resulted in a significant increase in specific growth rate and intestinal Lactic acid bacteria count compared to control (P<0.05). The increase of Protein efficiency ratio by increasing milkweed seed powder at the rate of 3 to 5% showed a significant difference with control, but there was no significant difference between experimental groups. The best results of survival rate, feed conversion ratio, hepatosomatic index and gastro somatic index were achieved in the treatments receiving 2, 3, 4, and 5% milkweed seed powder (P<0.05). The results showed that an inclusion of maximum 3% milkweed seed powder as an herbal feed additive could be an appropriate candidate in the diet of rainbow trout.