The immediate early 1 (ie-1) gene is essential for DNA replication of nucleopolyhedrosis virus. Here, the gene ie-1 from nucleopolyhedrovirus (Nanglai-BmNPV) infecting a local silkworm (Bombyx mori), Nanglai strain, was cloned and sequenced. The gene contained a 1755 bp open reading frame encoding a deduced protein of 584 amino acids, molecular weight 66.9 kDa, and isoelectric point 5.79. The nucleotide and amino acid sequences of Nanglai-BmNPV ie-1 gene showed, respectively, 98 and 97% identity to those of the BmNPV ie-1 genes. The identity of the Nanglai-BmNPV IE-1 deduced amino acid sequence with IE-1 protein sequences of other 37 known Lepidopteran NPVs varied from 20% up to 97%. The phylogenic tree established with the IE-1 protein sequences of the Lepidopteran NPVs showed similar topology to those previously reported using highly conserved genes. Interestingly, the tree obtained with IE-1 clearly shows that the Lepidopteran NPVs group II clade can be subdivided into three subgroups.