The Euonymus defoliator moth, Pryeria sinica Moore (Lepidoptera: Zygaenidae), is a pest that causes considerable damage to the Euonymus genus, especially Euonymus alatus and Euonymus japonicus. The biological characteristics of P. sinica have been studied in China, Japan, Taiwan, and the United States, but there has been no research conducted on this species in Korea. Also, P. sinica has two dormant phases in each generation, one as eggs in winter and the other as pupae in summer. Our purposes are to study the biological characteristics of Korean populations of P. sinica and to examine the effects of temperature and photoperiod on summer diapause. The biological characteristics were investigated in laboratory conditions (25 ± 1 ℃, 65 ± 1% R.H., 16L:8D) and the number of eggs in an egg mass, developmental periods and mortality rate in each larvae stage, and adults’ life span were determined. The results showed that 190.7 ± 31.64 eggs were contained in one egg mass and it took 25.57 ± 0.61 days from 1st larval stage to the pre-pupal stage. P. sinica has 4 larval stages and each stage took 4.28 ± 0.21, 6.2 ± 0.55, 6.02 ± 0.68, and 8.93 ± 0.88 days. The mortality rate of larvae peaked at 22.5% in 3rd larval stage. The adults’ life span was 4.67 ± 0.97 days in males and 4.61 ± 1.82 days in females. To study summer diapause, we divided pupae into 4 groups. Both low temperature and short daytime were effective in shortening the pupal stage. The pupal stage was the shortest in group D (122.12 ± 1.24 days), in which the initial condition was 25 ℃-16L:8D and the altered condition was 16 ℃ -12L:12D, and the longest in group A (161.92 ± 3.15 days, 25 ℃-16L:8D). These data could be utilized to propose the optimal timing for controlling the population of P. sinica.