Abstract: The insecticidal toxin showing effective virulence to aphids was isolated from the broth of Verticillium lecanii. In this paper, the virulence of this toxic substance against growth of Pieris rapae was conducted by injecting it into 5 instar larvae. The results showed that this toxic substance could effectively inhibit the development of the larvae (60.20%), and make them develop into malformed pupae, even lead death. The ultimate killing rate of this toxic against Pieris rapae was 83.3%.