Antifungal activity of caproic acid against Botrytis cinerea was investigated in this research. In vitro 200 ppm of caproic acid was inhibited on the germination and the mycelium growth of B. cinerea. 250 ppm of caproic acid showed the fungicidal activity against sensitive B. cinerea. To compared the inhibitory effect of treatments against B. cinerea, the field essay was carried out in the grape vineyard. The rot (%) of control, 3000 ppm of caproic acid, 3000 ppm of sodium caproate, and sumisclex were 30.7%, 10.2%, 22.8%, and 3.1%, respectively. The anti-Botrytis efficiency (%) was also evaluated as follows; 3000 ppm of caproic acid 66.8%, 3000 ppm of sodium caproate 25.7%, and sumisclex 89.9%. The efficiency between sumisclex and 3000 ppm of caproic acid was no significant difference at the 1% level by Tukey test. These results suggest that 3000 ppm of caproic acid may be greater than that of sodium caproate.