Abstract: The effects of testosterone, estradiol and the combination of the two hormones on the main development stages and population growth rate of Asplanchna brightwelli were studied with ecological experiment methods. The results showed that the 48h LC₅₀ of testosterone (T) was 9.56 mg/L, Y=1.9793X+3.0591 (R²=0.9211); 48h LC₅₀ of estradiol (E) was 8.18 mg/L, Y=3.5292X+1.7788 (R²=0.9195). Testosterone and estradiol significantly reduced the lifespan, the number of offspring, and population growth rate (r) except the condition under the concentration of 0.5 mg/L. Treatment with testosterone at the concentration of 8 mg/L significantly prolonged the pre-reproductive time by 11.71%, and decreased the lifespan and the number of offspring by 52.22% and 82.20%, respectively. Treatment with estradiol at the concentration of 8 mg/L significantly prolonged the pre-reproductive time by 7.10%, and decreased the lifespan and the number of offspring by 49.75% and 83.33%, respectively. When the two hormones were at a total concentration of 8 mg/L, compared with the control groups, the pre-reproductive period significantly prolonged by 34.17%—48.01%; the mean life significantly shortened by 31.56%—42.12%; the number of offspring reduced by 24.44%—80.33%. At the 5d, the population growth rate of rotifers significantly declined by 30.00%, 37.14%, 41.43%, 60.00% and 65.71% when they were exposed to T₆E₂, T₄E₄, T₈E₀, T₀E₈ and T₂E₆, respectively. Consequently, testosterone and estradiol showed significant effects on the durations of different development stages of Asplanchna brightwelli and the characteristics of its population growth. Simultaneously, the two hormones showed synergistic effects and the rotifers were more sensitive to estradiol.