Abstract: This study attempted to find a microorganism that could be effectively used for the bio-control of the major pestinsect, Phyllotreta striolata, on vegetables.Metarhizium anisopliae is known as apathogenic fungus that infects the pest. This experimentation evaluated the virulence of 8 M. anisopliae strains against P. striolata. One strainthat exhibited a high activity was Ma6. The bioassay showed a LT₅₀ on adult P. striolata inoculated with 8.0×10⁸ Ma6 spores·mL^-1 at 25℃ to be 4.09 d, and a 100% cumulative mortality rateat 25℃ for 7 d. It was, thus, concluded that Ma6 could be a potential candidate for the pest control. Subsequently, studies showed that the optimum medium for the hyphal growth and sporulation of Ma6 was PDA at 25℃ and pH 7.0 with 6 d in the dark followed by 8 d of sun exposure.