This work aimed to evaluate the pathogenicity of the UFMS 03 strain of Metarhizium rileyi to the Spodoptera cosmioides caterpillars under laboratory conditions. The experimental trial consisted of a completely randomized design, with six treatments. Each treatment consisted of 10 repetitions, containing five S. cosmioides caterpillars, standardized in 3 mm in length. The S. cosmioides caterpillars were placed inside Petri dishes and sprayed with the aid of an adapted Poter Tower, at a pressure of 15 pounds / inch, using 1 mL of the concentrations 1.0×1010, 1.0×109, 1.0×108, 1.0×107 and 1.0×106 conidia mL-1. Afterwards, the plates were sealed with pvc film and placed in an air-conditioned chamber at 25±1 °C, 70±10% RH, and a 12-hour photophase. Mortality was verified 24 hours after spraying. The concentrations of the M. rileyi strain UFMS 03 proved to be efficient, with emphasis on the concentration 1.0×108 conidia mL-1 showing 98% efficiency, in less lethal time (14.11 days). These results show the strain UFMS 03 of M. rileyi as a control agent for S. cosmioides.