Baculoviral anti-apoptotic genes, p35 and iap (inhibitor of apoptosis), play important roles in the initiation stage of viral infection. However, some iap genes are not involved in the anti-apoptotic activity. To investigate the anti-apoptotic activity of the iap genes of Lymantria xylina multiple nucleopolyhedrovirus (LyxyMNPV), two ly-iap genes (ly-iap2 and ly-iap3) were cloned from LyxyMNPV. From a 5′ RACE analysis, a late promoter motif (TAAG) was found in the upstream (-15 bp) of ly-iap2, but ly-iap3 only posited an enhancer-like element (CGTGC) in the upstream (-22 bp) of 5′ UTR. Gene expression were detected by RT-PCR; the ly-iap2 and ly-iap3 genes began to express in the host cells (IPLB-LD652Y cell line) infected with LyxyMNPV 6 hours post-infection (p.i.) and reached the peak 72 hours p.i., followed by decline 3 to 5 days p.i. Functional assay of the iap genes were performed by an over-expression method in Sf9 cells. Full-length domains of LY-IAP2, LY-IAP3 and LY-IAP2-BIR could differently inhibit the apoptosis which induced by Drosophila RPR protein (DRPR). Interestingly, LY-IAP2-RZF domain was important for LY-IAP2 to rescue apoptosis, but it might be also involved in the ubiquitin activity leading to the degradation of LY-IAP2 protein. LY-IAP3-RZF might be working as a “helper domain” to inhibit DRPR-induced apoptosis. These results can be used to figure out the roles of the ly-iap genes in the apoptosis of host cells.