The present study was performed to determine the effect of Yeast RNA on the synthesis of muscular protein in golden fish. There were 64 male fish allotted into four groups with 16 in each, chosen by random. Group (1) was used as the control, while the other three groups (2, 3, 4) were injected intra-abdominally with 0.5ml of nucleic acid solution which contains 2, 4 and 8mg yeast RNA per ml water. Injections were made once each week, 4 fish from each group being sacrificed for the purpose of determining the contents of muscular protein on the 7th day after each injection. The muscular protein was measured by the Kjeldahl method. The results reveal that the muscular protein contents of the fish from the experimental groups (2), (3) and (4), were 15.72%, 15.69% and 43.89% higer respectively than those in the control group.