The newly hatched nymphs of brown planthopper(BPH) were reared individually for two generations in test tubes, where young rice seedling was planted on agar solution, at $30^{circ}C,;25^{circ}C;and;20^{circ}C;with;95\%,;75\%,;65\%;and;35\%$ R.H. Effects of $30^{circ}C$ on the development of BPH when compared with those of $25^{circ}C$ are followings. Egg period, nymphal period, and adult longevity were shortened. Nymphal mortality was increased and the number of oviposited eggs was decreased. Hatchability was zero per cent because the eggs were either unfertilized or died before finishing the development. At the low temperature of $20^{circ}C$, in comparision with $25^{circ}C$, the developmental period of nymphs and eggs was considerably lengthened, and adult longevity was shortened, the number of oviposited eggs was decreased. The nymphal mortality was higher at high relative humidity $(above;75\%;RH)$ than that at low relative humidity $(under;65\%;RH)$. Under the condition of high relative humidities, the adult longevity was shortened, and the number of oviposited eggs was decreased.