This paper reports a plate assay to detect activities of polygalacturonase and cellulase secreted by Fusarium oxysporum f. sp. cubense (FOC), which is the most destructive pathogen of banana. The optimum cultural conditions for the polygalacturonase production were using pectin as induced substrate to inoculate with 1×10 ₄ mL^-1 conidia of FOC and after being cultured for 3 days. The optimal temperature of polygalacturonase activity was 37 ℃. The optimum cultural conditions for cellulase production were using carboxymethyl cellulose (CMC) as induced substrate to inoculate with 1×10 ₅ mL^-1 conidia of FOC in inducing medium after being cultured for 3 days. The optimal temperature of cellulase activity was 37 ℃. Based on the method, two mutants with impaired polygalacturonase and cellulose activity were attained through screening virulence-reduced mutants of FOC.