Biology of Menochilus sexmaculatus Fab. and Coccinella undecimpunctata L. on alfalfa aphid Therioaphis trifolii Monell were investigated during winter season at Tando Jam, Sindh, Pakistan. The latent period of M. sexmaculatus was 31.7$pm$0.3 and C. undecimpunctata 6.7$pm$0.1 seconds. Duration of copulation in M. sexmaculatus and C. undecimpunctata were 81.8$pm$5.4 and 64.5$pm$6.1 minutes. The oviposition and post-oviposition period of M. sexmaculatus, were 27.4$pm$4.1 and 4.5$pm$0.3 days and C. undecimpunctata, were 19.9$pm$5.2 and 3.8$pm$0.4 days. Fecundity per female was observed 602$pm$75.3 for M. sexmaculatus and 761$pm$85.2 for C. undecimpunctata. The mean egg periods of M. sexmaculatus and C. undecimpunctata were 8.6$pm$1.2 and 7.3$pm$1.0 days. Larval duration for first, second, third and fourth instars of M. sexmaculatus were 7.3$pm$0.6, 4.3$pm$0.2, 3.8$pm$0.3 and 6.7$pm$1.1 days. The pupal period of M. sexmaculatus was 3.6$pm$0.3 and C. undecimpunctata was 5.1$pm$0.5 days. The adult period of M. sexmaculatus, (female and male) under this study was 34.9$pm$4.8 and 29.7$pm$1.2 days.