Abstract: The polymerase chain reaction ( PCR) method for detecting Ectropis obliqua multip le nuclear polyhedrosisviruswas established with self2designed p rimers according to the sequence of polyhedron gene of EoNPV, andEoNPV could be detected from the offsp ring, the data showed that the method would allow the detection of about 1fg, thismethod could be used to identify EoNPV in field p ractices. The method was simp le with good rep roducibilityand selectivity, and high sensitivity, so deserves to be popularized. An infectivity test of EoNPV against the secondinstar larvae of Ectropis oblique was carried out in our laboratory, and LC50 of EoNPV was determined as 2. 2 ×104P IB·mL -1 , the larva was very sensitive to EoNPV, and it had a higher death rate with higher EoNPVconcentration, and the death time p resented positive correlation with the concentration of EoNPV.