A rapid and sensitive detection of BmNPV contamination in silkworm rearing room was carried by Plymerase chain reaction(PCR). Silkworm nuclear polyhedra were dissolved for the extraction of viral DNA within 30 minutes followed by the treatment of alkaline solution. The combination of primers of NP3 and NP2 was superior in PCR to the other 7 primers applied. Each primer was designed with 20 base in size and Newly designed NP3 of sense and the already reported NP2 for antisense were better in reaction than other primers. PCR products appeared 500bp in size. And annealing was confirmed proper at 55$^{circ}C$ condition. Amplifiable template DNA amount was confirmed at least 100 ng to 0.1 ng and regarded as applicative for the assay of silkworm rearing environmental condition of sericultural farm. In case of the detection of BmNPV from the dust, sensitivity by PCR was as high as 1,000,000 times than that of microscopic observation.