The grey mullet fingerling were imported to Iran in 1997 from Hong Kong and in coastal fish pond of north part of Iran were successfully cultured in order to obtain broodstocks and induce artificial reproduction. Seasonal changes in serum concentrations of Testosterone, 17-β Estradiole (E2), 17-α Hydroxy Progesterone and also the level of calcium, Triglyceride and cholesterol in females grey mullet in captivity were measured by Radioimmunoassay or colorimetry, respectively. Investigating of sex steroids in different sexual maturity indicated that increasing of oocyte diameter and sexual maturity development serum testosterone was increased significantly (P<0.05). Although Biochemical parameters concentrations in blood serum of grey mullet diminished significantly until third stage of sexual maturity (P< 0.05), their level showed a rising trend at the fourth stage. A significant increase was observed in the serum protein and cholesterol concentrations (P<0.05), while, in contrast, serum Calcium ion and triglyceride levels didn’t have significant differences in third and fourth stages of sexual development (P> 0.05). These results suggest that the seasonal changes in serum lipids and gonadal steroids were associated with reproductive development. The data also support the hypothesis that the shortening photoperiod is a major factor in stimulating reproductive activity in striped mullet.