Chilo suppressalis(C. suppressalis) larvae were treated with Metarhizium anisopliae(M. anisopliae) CQMa421 preparation at the recommended field dose of 1.6×107 cells/mL. The toxicity of M. anisopliae CQMa421 preparation to C. suppressalis larvae as well as the larval total protein content and activities of catalase(CAT), peroxidase(POD), superoxide dismutase(SOD), carboxylesterase(CarE), acetylcholinesterase(AChE), alkaline protease(AKP) and glutathione S-transferases(GSTs) were determined. The results showed that the survival rate of C. suppressalis larvae showed a continuous decreasing trend after treatment with M. anisopliae CQMa421 preparation, preparation with the LT50 of 7.23 d and the mortality rate of 56.89% on the 10th day of treatment, indicating that the M. anisopliae CQMa421 preparation had significant toxicity to C. suppressalis larvae. The protein content of C. suppressalis larvae was the highest at 3 d of M. anisopliae CQMa421 preparation treatment. At 2, 4 and 5 d after treatment, the activities of three protective enzymes, POD, CAT and SOD, reached the highest with 198.76, 19.59 and 12.90 U/mg, respectively, which were significantly higher compared to the control. The highest activities of four detoxification enzymes, GSTs, AChE, CarE and AKP, were 1.68, 1.68, 1.27 and 1.62 times higher than those of the control, respectively. The results indicate that the homeostasis of C. suppressalis larvae was disrupted by the treatment of M. anisopliae CQMa421 preparation, which in turn exerted a toxic effect on the larvae.