Temperature-dependent development of eggs, larvae, and pupae of the speckled green fruitworm, Orthosia hibisci Guenée, at constant temperatures of 5–30.0 °C, 7.5–27.5 °C, and 0.8–20.8 °C, respectively, was described. Development times decreased with increasing temperatures and minimum developmental times in eggs, larvae, and pupae occurred at ca. 27.5, 25, and 20.8 °C, respectively. Variation in development times of all life stages was modelled accurately (R2 values 0.98–0.99) with a Weibull distribution. Relationships between temperature and developmental rates of all life stages were described by linear degree-day (DD) and nonlinear poikilotherm models. There were significant differences (ANOVA, P < 0.05) among the slopes of regression equations describing developmental rates of different life stages and larval instars. Minimum developmental temperatures for eggs (3.4 °C), first- through fifth-instar larvae (4.7, 2.9, 3.6, 3.5, and 3.7 °C), and pupae (2.8 °C) were determined by extrapolation of linear regression equations to the x-intercept. Median development time of eggs, first- through fifth-instar larvae, and pupae required 99.0, 44.2, 51.5, 52.4, 57.1, 69.9, and 61.3 DD above the minimum developmental temperatures, respectively. Developmental rates of eggs and all larval instars averaged were described by six-parameter models exhibiting low- and high-temperature inhibition. Development of pupae was best described by a four-parameter model exhibiting low- but no high-temperature inhibition. This information should be useful for developing a phenology model to improve management actions against O. hibisci.