A novel cloned Spodoptera littoralis Nucleopolyhedrovirus (SlNPV) p49 gene is able to suppress apoptosis of insect cells Sf9 triggered by virus. The amino acid sequence of P49 expressed in baculovirus expression system is the same as predicted, indicating that the expression of P49 is correct. Metabolic labeling revealed that p49 was able to be expressed both in the early and late phases after the viral infection, and only in the late phase was the expression driven by polyhedra promoter, but the amount of expression was higher than that of wtSlNPV. In summary, the early gene of SlNPV p49 as well as p35 of AcMNPV is able to be expressed in the late phase, but its promoter is weaker compared with polyhedra promoter. In vitro, P49 can be cut by Bm caspase and human caspase-3, yielding 10 and 40 ku fragments. Purified P49 blocks the substrate cleavage by Bm caspase and human caspase-3, showing that P49 inhibits downstream caspases in the apoptotic pathway.