Abstract: Serum levels of sex steroids of silver carp (Hypophthalmichthys molitrix) were measured during induced ovulation with mamalian luteinizing hormone-releasing hormone analogue (LHRH-A) and human chorionic gonadotropin (HCG). The changes of serum concentration of testosterone (T) and 17α 20βp-dihydroxyprogesterone (17α 20βp) were found after injection. Oestradiol (E2) and progesterone (P) concentrations were low throughont the period of induced ovulation. Both inducing agents stimulated T to reach peak level (4.83-16.65 ng/ml) rapidly. Ovulation occurred when 17α 20βp reached to peak level (4.35-5.30ng/ml) and T declined. E2 level was low and showed no significant change. All these indicate that gonadotropin induced maturation of silver carp via the mediation of 17α20βP, which is the natural mediator of oocyte maturation in silver carp. This study provides a theoretical basis on applying 17α20βp as an agent for induced spawning of fishes.