The objective of our study was the formulation of a local strain of Mamestra brassicae nucleopolyhedrovirus-K1 (MabrNPV-K1) for the development of viral insecticide to control M. brassicae. To formulate MabrNPV-K1, feeding toxicities of various supplements and ultraviolet (UV)-protection were investigated. Optical brightener Tinopal UNPA-GX (Tinopal) as UV protectant and Bentonite had some toxicity themselves to increase the mortality. The protection of polyhedra from UV light radiation was observed only by Tinopal. The MabrNPV-K1 was formulated as a wettable powder form. The mortality of the formulation was higher and rapid than that of the un-formulated. This suggested the possibility of MabrNPV-K1 formulation as an effective biological control agent for M. brassicae.