The diamondback moth, Plutella xylostella is a one of the most important pests of various cruciferous crops and has a geographically wide ranging habitat. The heavy dependence on chemical pesticides has created severe pesticide resistance problems. In recent years, Bacillus thuringiensis product have been widely used for P. xylostella control bus genetic resistance in populations to some B. thuringiensis strains, compounded by cross-resistance to several different B. thuringiensis toxins, has also been identified. Such recent resistance problems serve to emphasize the urgent need for alternative control agents and their use within an integrated pest management approach. Baculoviruses have been used as agents for the biological control of certain insect pest species. the granuloviruses (GVs), based on the structure of the occluded virus and the occlusion body (OB). Several reports have showed P. xylostella granulovirus (PxGV) as a promise control agent for P. xylostella. However, it is very difficult to study GV because its OB, granule, has very small size and could be observed exactly under the electron microscopy (EM). This study was performed to develop rapid quantification method for granule of PxGV. After the exact quantification of granule with latex beads using EM, the universal extraction method of viral DNA was established for consistent experiment. The number of granules was calculated by the quantification of PCR products for granuline gene using spectrophotometer and densitometer. This novel calculation method for granule would be useful to study GV.