Phaedon brassicae is a serious pest of brassicaceous vegetables in Japan and China, but the effects of thermal changes on development, survival and reproduction is not well demonstrated. In this study, effects of constant temperatures and thermoperiods simulated alternating high summer temperatures on the development, survival and reproduction were examined in this beetle at 12L:12D. At constant temperatures, egg hatch and survival of larvae and pupae were highest at 28, 24, and 24°C respectively. Within the range of 12–30°C, the developmental periods of immature stages decreased significantly with increasing temperature, but a delay in development was observed at 30°C. The developmental zeros were estimated at 7.1, 6.9 and 7.1°C and thermal constants of 87.7, 178.6 and 68.0 degree-days were estimated for the development of the eggs, larvae and pupae, respectively. Adult longevity decreased with increasing temperature, but there were no significant differences among temperatures (16–28°C). Fecundity at 24°C (768.68 ± 385.44 eggs per female) was significantly greater than at other temperatures. The optimal temperature is approximately 24°C. Moreover, high alternating temperatures had little effect on egg hatch, but higher thermophase (6 h) temperatures retarded the survival of larvae and pupae. No individual survived to eclosion at thermoperiods with thermophase temperature of 38°C. High temperatures (above 34°C) lasting several hours had detrimental effects on survival, development and reproduction in P. brassicae.