The insect nervous system contains biogenic amines such octopamine (OA),which is synthesized from tyramine (TA) by catalysis of tyramine-${eta}$-hydroxylase ($T{eta}H$). In this study, the Drosophila 70 kDa tyramine-${eta}$-hydroxylase ($DmT{eta}H$) protein was purified after the recombinant nucleopolyhedrovirus isolated from Bombyx mori (BmNPV) containing the $T{eta}H$ gene was injected into the hemocoel of the fifth instar larvae from the d17 B. mori strain. Western blot analysis revealed an immunoreactive band with a molecular mass of 70 kDa. The products formed by incubating the enzyme reaction mixture were separated and detected by reverse phase high-performance liquid chromatography. The optimum pH, temperature, and incubation time for the conversion of TA to OA were 7.6, $25^{circ}C$, and 30 min, respectively. The inhibitory experiments using various concentrations of 1-(2-methoxy-5-methylphenyl) imidazole-2(3H)-thione (MMIT) showed that MMIT inhibited $DmT{eta}H$ dose-dependently and that this method can be applied for screening $DmT{eta}H$ inhibitors.