Homologues of Helicoverpa armigera nucleopolyhedrovirus (HearSNPV) orf33 are found in all 22 completely sequenced members of the lepidopteran nucleopolyhedroviruses and granuloviruses, but so far their functions are unknown. In this report, we describe the characterization of HearSNPV orf33 (ha33). Northern blot analysis showed a single transcript of ha33 of approximately 0.7 kb was transcribed beginning at 3 h post-infection in infected Helicoverpa zea cells (HzAM1) and the gene product could be detected as early as 6 h post-infection by western blot analysis using a rabbit derived polyclonal antibody, suggesting it was an early gene. Western blot analysis also demonstrated the ha33 protein in infected cells was a 31 kDa protein, larger than the theoretical size of 28.4 kDa, and located in the envelope fraction of budded virions (BVs). The results suggested that HearSNPV ha33 gene is a functional gene that encodes a novel structural protein of baculovirus BVs, BV-e31.