We tested the bioactivity bioinsecticide of Beauveria bassiana –G07 /Bassiana muscardin/ against the Jacobson's spanworm /Erannis jacobsoni Diak/, which is the most destructive pest in the forest. The experiment was conducted 5 variants (1.5×106 spore/ml, 1.5×107 spore/ml, 1.5×108 spore/ml, 1.5×109 spore/ml, control), 3 times on the larvaes in the laboratory in 14 days. For the field experiment, we used 4 variants (1.5×1013 spore/he, 2.5×1013 spore/he, 3.5×1013 spore/he, control), 3 times in 21 days. From the result of laboratory study the 1.5×109 spore shows 91.9% bioactivity, and in the field study 3.5×1013 spore/he shows 80% bioactivity. Local strain B. bassiana –G07 and cultures of B. Bassiana, which were isolated from larvaes, died during the laboratory experiment, were detected and it was identified as species B. bassiana by PCR.