The protease in polyhedral virus particules shows the highest activity at about pH 11 and is destroyed by heating at 80℃ for 10 minutes. This viral protease is inactivated by copper sulphate of high normality, p-chloromercuribenzonic acid, flavin adenine dinucleotide, chloramphenicol palmitate, nitromin, nitrogen mustard, aureomycin or potato inhibitor, and activated by copper sulphate of low concentration, thiourea or ascorbic acid. The proteolytic action, however, is not influenced by theophylline, sodium azide, ethylendiamine tetraacetate, monoidoacetic acid, chloramphenicol, 8-azaguanine, mitmycin and carzinophillin.