Larval development, adult longevity and oviposition of the beet armyworm, Spodoptera exigua H bner was studied at 16, 20, 25 and 3$0^{circ}C$ with a 16L: 8D photoperiod. Egg hatchability of S. exigua was the highest at 3$0^{circ}C$ and reduced with decreasing temperature. Egg period was the shortest at 3$0^{circ}C$ and prolonged with decreasing temperature. Percent pupation was became higher at higher temperature form 23.2% to 94.0%. Developmental period of larva was the shortest at 3$0^{circ}C$, but extended with decreasing temperature. Adult emergence ratio was the highest at 3$0^{circ}C$ and reduced with decreasing temperature. The mean pupal period was 35.2, 14.4, 7.8 and 5.0 days at 16, 20, 25 and 3$0^{circ}C$, respectively. Relationships between constant temperature and the developmental velocity of egg, larva and pupa were linear. Developmental threshold temperature seems to be 13.3 8$^{circ}C$ for egg, 14.02$^{circ}C$ for larva, 14.09$^{circ}C$ for pupa, and 13.84$^{circ}C$ for egg the adult. Estimated value of the total effective temperature for completing each stage was 36.89 day-degree for egg, 155.72 day-degree for larva, 79.20 day-degree for pupa, and 273.41 day-degree for egg to adult. Female longevity varied to temperature from 11.4 days at 16$^{circ}C$ to 5.8 days at 3$0^{circ}C$, and male longevity was longer than that of female. Preoviposition period was the shortest at 3$0^{circ}C$, but prolonged with decreasing temperature. It was about 2.7 times longer at 16$^{circ}C$ than that at 3$0^{circ}C$. Number of eggs per female was the highest at $25^{circ}C$, followed by 20, 30 and 16$^{circ}C$.