The annual changa of gonadotropin (GTH) a.nd estradiol--17 (E₂) level in the serum of male and female common carp (GyPrinus curpio L) were mea-eared by radioimmunoassy(RIA). The annual average level of GTH in female carp was 8.94 a-5.94 ng/ml, with minimum 1.17+0.76ng/ml in December, and maximum 21.50+11.82 ng/ml in January. The anneal average of GTH level in male carp was 8 .72+5.20ng/mI. minimum 4 .74+2. 81 ng/ml in December and maximum 16.00+7.10 ng/ml in 1lovember. gerund E₂ level in female rises from Janusry to April,the average level is 2019.48+754.49 pg/ml while the peak level is 3215.78 +206.34pg/ml in Feberay. The ovaries regressed soon aftor spawning season and E₂ level significantly decreased to 454.58 pg/ml from May to August. The difference is obvious between prespa..wning rind postspawning seasons (P= 0 .001). These results indicate that the development and maturation of gonads are closely related to the change of serum E₂ Ievel. The feedback effect of E₂ on function of pituitary is also discussed.