[Objectives] To determine the toxicity of the Beauveria brongniartii strain NEAU30503 to larvae of the spotted and black cutworm. [Methods] The leaf dipping method was used to determine the toxicity of NEAU30503 to young cutworm larvae and the soil treatment method to determine its toxicity to older instar larvae. [Results]  The toxicity of NEAU30503 to 5-day-old larvae of spotted cutworm at day 15 post infection can be expressed by the regression equation y=0.6568x－0.1636 (r=0.9846). The LC₅₀ and LC₈₀ were 7.28×10⁷ conidia/mL and 139.14×10⁷ conidia/mL, respectively. The toxicity of NEAU30503 to 5th instar spotted cutworm larvae can be expressed by the regression equation y=1.0929x－3.2893 (r=0.9801), with LC₅₀ and LC₈₀ of 3.85×10⁷ conidia/L and 22.65×10⁷ conidia/L, respectively. NEAU30503 was lethal to cutworm pupae, and clearly decreased the eclosion rate of cutworms. When NEAU30503 was mixed with tea saponin, the sublethal dose of beta-cypermethrin and abamectin could significantly increase the toxicity to black cutworms. [Conclusion]  The NEAU30503 strain was the most toxic to cutworms. NEAU30503 was more toxic to older instar larvae when delivered via the soil. When sprayed, a mixture of NEAU305035 with a sublethal dose of beta-cypermethrin or tea saponin had a significant effect on young cutworm larvae. This study provides a scientific basis for using Beauveria sp. to controll cutworms in the field.