Apoptosis was induced in Spodoptera litura Sl-zsu-1 cells transfected with plasmid pAcie-1 DNA containing ie-1 gene of Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV). Apoptotic bodies appeared 24 h post transfection and cell mortality peaked after 48 h. Electrophoresis of total DNA extract of Sl-zsu-1 cells showed a DNA ladder, indicating that transfection of ie-1 gene alone can trigger apoptosis directly or indirectly. It was shown by cytochalasin D (CD) and ammonium chloride inhibition assays that the entry of virions into cytoplasm was required for induction of apoptosis. Reverse transcriptase PCR (RT-PCR) was used to demonstrate that ie-1 gene had transcribed in Sl-zsu-1 cells immediately after infection. Inhibition of DNA replication could not block the cell death process, suggesting that this apoptosis was independent on viral late replication events. Apoptosis did not occur when Sl-zsu-1 cells were infected with an AcMNPV mutant tsB821 at its nonpermissive temperature. Therefore, we concluded that the ie-1 gene is at least one of the factors inducing apoptosis in Sl-zsu-1 cells infected with AcMNPV.