The life history and predation rate of Lemnia biplagiata (Swartz) fed on Aphis gossypii Glover was studied at 25°C in the laboratory. The raw data were analyzed based on the age-stage, two-sex life table to take the variable developmental rate among individuals and both sexes into consideration. The intrinsic rate of increase (r) is 0.1570 d⁻¹, the finite rate of increase (λ) is 1.170 d⁻¹, the net reproduction rate (R₀) is 291.1 offspring per individual, the mean generation time (T) is 36.2 d, and the gross reproduction rate (GRR) is 604.8 offspring. L. biplagiata consumed 430 ± 42 aphids (mean ± SD) during the larval stage. The mean consumption rate for an adult during the first 25 d (aged 14–38 d from birth) is 1,548 ± 118 aphids. The mean consumption for an older adult (aged 60–119 d from birth) is 1,319 ± 1,259 aphids. When the survival rate is taken into account, the net consumption rate is 3,022 aphids per individual during the total life span. The transformation rate from prey population to predator offspring is 10.4. The relationship among GRR, R₀, and the preadult survival rate (l_a) is proven as R₀ < l_a · GRR < GRR. However, when applying the female age-specific life table to a two-sex population, due to the difficulty in determining the preadult mortality of the females, the calculated age-specific survival rate and fecundity are possibly incorrect and consequently the relationship among GRR, R₀, and l_a also may be incorrect.