Excessive scrotal heating or cooling may lead to the cessation of spermatogenesis. Data regarding heat exchange rates in scrotal skin can be used to control testicular temperature within the appropriate range. Heat flux (HF) in the scrotal skin surface is generated based on the surrounding environment. This study aims to elucidate the HF of scrotal skin by varying ambient temperature. Twenty college students including seven varicoceles volunteered as the subjects (mean age: 22.95 ± SD 1.96 years; height: 175.00 ± 5.17 cm; weight: 68.40 ± 8.65 kg; body mass index: 22.28 ± 2.15), and participated in the experiments from September 11 to October 4, 2006. The environmental temperature was controlled at 20 °C and 25 °C in the first and second experiment respectively. The HF and skin temperature on both sides of the scrotal surface were measured for 60 min in the environmental chamber. The results revealed that the HF was 87.64 ± 12.69 W/m2 and 78.91 ± 12.09 W/m2 in the left and right side of the scrotum respectively. The scrotal skin temperature (SST) was 30.28 ± 0.75 °C and 30.24 ± 0.62 °C on the left and right side of the scrotum in the 20 °C environment respectively. In the 25 °C environment the HF was 53.54 ± 8.86 W/m2 and 45.25 ± 8.32 W/m2, and the SST was 32.29 ± 0.61 °C and 32.07 ± 0.36 °C on the left and right side of the scrotum respectively. The cooling source power to decrease testicular temperature is suggested at 290 W/m2. This suggested value could be adopted a cooling device as clinical therapy for a heat stress patient to decrease testicular temperature affecting spermatogenesis.