This study was performed to produce monoclonal antibodies to the major polyhedral inclusion body (PIB) antigen of the occluded form of Hyphantria cunea nuclear polyhedrosis virus (HcNPV). PIB proteinS were purfied from the Spodoptera frugiperda cell infected with HcNPVs. Using the purified PIB protein, BALB/C mice were immunized 3 times with 2 weeks intervals. The spleen were removed and fused with Sp2/0-Ag14, mouse myeloma cells.