A plaque-purified genotypic variant, derived from a field isolate of the Malacosoma neustria nucleopolyhedrovirus (ManeNPV) from Turkey was characterized based oil in vitro replication properties in a cell line, Md203 derived from Malacosoma disstria. The life cycle of ManeNPV was studied based oil the cytopathic effects (CPEs), polyhedral inclusion body (FIB) formation, budded virus (BV) production, viral DNA replication and polyhedrin protein expression in ManeNPV-infected Md203 cells. Infection of Md203 cells with ManeNPV resulted in cytopathic effects within 24 and 36 h post infection and most cells detachted from the bottom of the culture plate oil the fourth day. Typical NPV cytopathic effects (CPE) like granulated and rounded cells, nuclear hypertrophy and impairment in cell proliferation, and lost cell shape with the extendings were observed. Budded viruses were detected at 24 h p.i. However, significant increase in BV production was observed after 48 h p.i. PIB was firstly detected at 36 h p.i. When BV's were used for reinfection of the Md203 cells, the result showed that these cells support production of viable virus progeny. We also observed a significant level of viral DNA synthesis by 24 h p.i. The results indicate that ManeNPV can be propagated at in vitro system for further studies and thus has a potential for development into an effective biotechnological and microbial insecticidal agent.