In recent decades, interest in using medical plants powders as growth factors and immunestimulants in aquaculture has been increased. This study was conducted to evaluate the effect of different levels of dietary supplementation of garlic, Allium sativum on growth factors and body composition of Molly Fish, Poecilia sphenops. Four diets containing supplementation at levels of 0, 5, 15 and 30 g kg −1 were fed to fingerlings of Molly Fish (initial weight, 0.85 g) in triplicates tanks three daily to apparent satiation for 56 days. The result of experiment showed, growth performance and feed efficiency were improved in all treatments compared with control group. But according to the results, the best final weight, weight gain rate (WGR%), specific growth rate (SGR) and food conservation ratio (FCR) were observed in the fish fed 15 g kg -1 A.sativum in diet. The highest protein content was obtained in the fish fed with dietary with 15 g kg −1 A.sativum powder. Also fat tissue of fish had significantly decreasing trend compared with control group. Moisture and ash contents were no significantly affected by A.sativum. The results of the present study indicated clearly that the supplementation of A.sativum (15 g kg −1 diet) enhanced the growth performance, feed utilization and body composition of Molly Fish, P.sphenops.