Abstract: To compare the conception rate of defined–time artificial insemination with frozen-thawed semen following estrus synchronization in autumn in cashmere goats and define the optimal insemination time to achieve a higher conception rate, the progesterone suppository, pregnant horse serum gonadotropin（PMSG） and PGF_2α were used to induce estrus and ovulation in Liaoning cashmere goats in this experinent. The does were divided into 1 control group and 4 experimental groups, which inseminated with 0.25 mL semen at 0 h, 6 h, 12 h, 18 h and 24 h following the onset of estrus through estrus synchronization, respectively. The results showed that the estrus rates were 86.67% in the control group and 83.33%, 90.00%, 86.67% and 83.33% in the four experimental groups, respectively. The conception rates were 15.38% in the control group, and 56.00%, 57.89%, 36.00% and 4.76% in the four experimental groups, respectively, with suggesting that the optimal insemination time could be at 6-18 h following the onset of estrus. In the screening test, the does following the onset of estrus used as the control group（at 6 h） and four experimental groups（at 9 h, 12 h, 15 h and 18 h） for frozen semen insemination. The results showed that no significant difference in estrus rate among the control group and four experimental groups was found（P ＞ 0.05）, and the conception rate was 59.25%, 66.67%, 57.69%, 44.44% and 32.00% in the control group and in four experimental groups, respectively, suggesting that the optimal time for frozen semen insemination could be at 9 h following the onset of estrus through estrus synchronization.