Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) is an important natural enemy of insect pests of agricultural importance. An artificial diet is needed when insects upon which the predators feed are in limited supply. Larval mortality, duration of larval development, duration of the pupal stage, and adult weight were compared for various concentrations of nine ingredients of an artificial diet in an L₉(3)⁴ multi-index orthogonal array design. A range analysis (“R” method) coupled with an integrated balance method determined that the theoretically optimal diet for P. japonica larvae was 6 g ground powder of Mythimna separata (Walker), 2 g yeast extract, 1 g sucrose, 0.08 g olive oil, and 29.42 g basic diet. After further testing, we found that this diet yielded a higher larval survival rate, longer larval period, longer pupal period, greater adult weight, and higher eclosion rate of P. japonica compared with the eight artificial diets tested.