Precise determination of insemination time is an important factor. However, the detection is intensive labor observing behaviors of sows. Previous researchers have tried to find indicators for easy detection of optimum time of insemination. The one of the indicators is change of temperature for estrous cycle. Therefore, this study was conducted to determined alteration of vulvar and rectal temperature in Duroc sows during estrus period for detection of optimum time of insemination. Experimental animals were twelve Duroc sows 2 parity for winter season. The sows were feeding 5 ml regumate (estrus synchronization agent) during 15 days, and then measured temperature of vulva and rectum when half day by thermal camera and thermometer. Also, conventional method was utilized as control. By the conventional method, estrus was identified at four days after ending supply of regumate. At the same time, temperature of the vulva and rectum was higher than other days. Average temperature in valva and rectum was 38.8 ℃ in estrous sows, wherease non-estrous sows were 38.7℃. This difference of temperature suggested feasibility as indicator inseminating optimum time. Henceforward, ummanned estrous detection system can be useful by economic improvement via reduction of labor in swine farm.