The present invention is to provide a composition for preventing plant diseases which comprises at least Component I and Component II, is capable of obtaining a synergic effect that cannot be expected with each single component, is capable of markedly increasing a control effect in a much smaller amount of chemicals against various plant pathogens, and causes no phytotoxicity suffering.A composition for preventing plant diseases comprises Components I and II as active ingredients. The Component I is (RS)-N-[2-(1,3-dimethylbutyl)thiophen-3-yl]-1-methyl-3-tri fluoromethyl-1H-pyrazole-4-carboxamide. The Component II, is picoxystrobin.
