Inactivation of Bombyx mori nucleopolyhedrovirus occluded virions (BmNPV OVs) was promoted by the synergistic effect of sodium hypochlorite (NaClO) and sodium carbonate (Na2CO3) mixtures. Bioassay results using silkworm neonate larvae demonstrated that BmNPV OVs in occlusion bodies (OBs) were inactivated at 100ppm of free chlorine when 0.1ml of the viral suspension (1.05×108 OBs/ml) was treated for 5min with 0.9ml of a 0.3% (w/v) Na2CO3-added solution of NaClO. This combination mixture showed a higher value of LC50 (108.30OBs/ml) than that of 2.5% formaldehyde (104.23OBs/ml) with a 5 min-chemical treatment. On the other hand, all the test larvae died of nucleopolyhedrosis when BmNPV OBs (1.05×108OBs/ml) were treated for 5min with 0.3% (w/v) Na2CO3 or three solutions of NaClO which contained free chlorine of 100, 250 and 500ppm. In order to confirm the practical use of the Na2CO3-added solution of NaClO, we also checked the pH stability and inactivation of BmNPV under circumstances of a lower pH created by adding the silkworm artificial diet into the combination mixture.