Wild-type AcMNPV (Autographa california multicapsid nucleopolyhedrovirus) induced Spodoptera litura (Sl-zsu-1) cells apoptosis at 10～12 h post infection, but it could undergo productive replication in Spodoptera frugiperda (Sf-9) cells. The AcMNPV anti-apoptotic gene, p35 gene replication and transcription in different cell lines (Sl-zsu-1 and Sf-9) were investigated by Southern dot blot and RT-PCR respectively. Differences for p35 gene to synthesize and transcribe in these two cell lines suggested that it could not significantly function in the non-permissive cell line due to its untimely and insufficient expression. Inoculation of Sl-zsu-1 cells with wild-type SpltMNPV (Spodoptera litura multicapsid nucleopolyhedrovirus) 12 h prior to AcMNPV infection blocked the apoptosis and rescued the AcMNPV productive replication. It is deduced that P49 protein, a P35 homolog encoded by p49 gene in SpltMNPV genome, might accumulate a certain level at 12 h post infection enough to counteract the caspases effect.