Abstract: We isolated a clone from Syngrapha falcifera multiple nuclear polyhedrosis virus (SfaMN- PV) by plaque purification and designated it as SfaMNPV-D. The SfaMNPV-D was very sensitive to 5B1 cell line and at 72h postinfection TCID₅₀ value of buded viruses was 3. 89 ×10⁸ TCID50/ ml and at 144h p. i the production of polyhedra was 4. 0 ×10⁷PIBs/ ml. Bioassay showed that LC₅₀ value of SfaMNPV-D was 7. 14 ×10⁵PIBs/ ml and LC₅₀ value of wild type SfaMNPV was 4.81 ×10⁶PIBs/ ml when early third instar larvae of Helicoverpa armigera that infected respectively by two viruses. When the third instar larvae of H. armigera were infected with SfaMNPV-D at the concent ration of 1.0 × 10⁶ and 1.0 ×10⁷PIBs/ ml , the L T₅₀ of SfaMNPV-D was 4. 9 and 4. 6d respectively. However , when the third instar larvae of H. armigera were infected with wild type SfaMNPV at the concent ration of 1.0 ×10⁶ and 1.0 ×10⁷PIBs/ ml , the L T₅₀ of SfaMNPV was 5. 5 and 510d respectively. sfaMNPV-D DNA was respectively cleaved with EcoR Ⅰ, Hind Ⅲ, B gl Ⅱ, Pst Ⅰand B am H Ⅰand molecular weight of virus genome was 113. 78 kb.