This study was conducted to evaluate the efficacy of live food (Artemia urmiana) and commercial diet in rearing of Oncorhynchus mykiss larvae. Experiment started when larvae were 0.12g in weight. Triplicate groups of fish were offered one of four treatments: (1) a commercial starter food (2) live Artemia urmiana nauplii (for 3 days) (3) live Artemia urmiana nauplii (for 7 days) and (4) combination of live Artemia nauplii (5% of food) and the commercial starter food. They were fed four times daily starting at the onset of exogenous feeding, for 1 week. After 1 week, the fish of all groups were shifted to the commercial diet for an additional 3-weeks period to determine the impact of any differences in weight of fish. The result of the present study showed that those larvae fed with combination of Artemia nauplli and a commercial starter food grew significantly faster than other groups for 4 weeks. Larvae fed with other composition were similar in length and weight (P>0.05). Survival rates of the trout larvae ranged 86-96% after 1 week and 67-84% after 4 weeks. Larvae survival after 1 and 4 weeks were significantly higher (P<0.05) in trout larvae fed only on Artemia nauplii (treatments 2 and 3) than other treatments. The body chemical composition analysis of trout larvae showed only small differences, with the exception of the crude protein and lipid at 4 weeks. The data were analyzed to determine significant differences among treatments by one-way ANOVA. (Statistica v.9, StatSoft Inc.).