The seasonal fluctuation of the large 28-spotted lady beetle, Henosepilachna vigintioctomaculata (Motschulsky), was observed in potato fields of Gangneung region, Gangwondo Province. The effects of their leaf consumption over a 24 hour period and developmental periods by different temperatures were investigated, and then the developmental threshold (DT) and effective cumulative temperature (ET) of each stage were calculated. Various developmental stages of H. vigintioctomaculata were captured in the fields from May to September, with three peaks in late May, late June, and late August. Leaf consumption by larval stages increased with the development of instar. The 4th instar larvae consumed potato leaves much more than other stages. Egg hatchability and emergence rate of H. vigintioctomaculata were lower at $10^{circ}C$ and $30^{circ}C$, but higher at around $20{sim}23^{circ}C$. The developmental periods of each stage became shorter as temperature increased; 90 days at $10^{circ}C$, 40 days at $20^{circ}C$ and 25 days at $25^{circ}C$. Base on developmental velocity to temperature, calculated DT and ET were $7.3^{circ}C$ and 83.