[Objectives]  To investigate the potential of using the fungal strain Metarhizium rileyi SZCY200812, isolated from infected Spodoptera frugiperda larvae in corn fields in Shizong county, Yunnan province, as a biological control for S. frugiperda. [Methods]  The growth rate and spore yield per unit area of the SZCY200812 strain were measured to evaluate its growth under different conditions. Its tolerance for different environmental factors was assessed based on the conidial germination rate. [Results]  M. rileyi SZCY200812 was highly virulent to S. frugiperda larvae; cumulative mortality of 3rd and 5th larval instars reached 100 % after 6 d and 8 d, respectively, with respective LT₅₀ values of 3.89 d and 4.66 d, respectively. The mycelial growth rate of M. rileyi SZCY200812 cultured on SMAY medium at 25 °C and L︰D=24︰0 was (1.68±0.01) mm/d on the 15th day, and the spore yield per unit area was (8.05±0.37) × 10⁷ conidia/mm². The maximum thermal and UV tolerances of SZCY200812 were 70 ℃ and 12 min, respectively. The temperature and UV tolerance of conidia produced under these conditions were the best. Under these conditions, the LT₅₀ of 3rd instar larvae treated with a conidial suspension of 1×10⁸ spores/mL was 3.26 d. [Conclusion]  The SZCY200812 strain is more tolerant to short-term exposure to high temperature and ultraviolet radiation than other M. rileyi strains, and could therefore be used to develop an additional biological control agents for this pest.