Abstract: The inhibitory activity of cymoxanil, mancozeb and their mixtures on Phytophthora infestans tested at different stage, in vitro, showed that cymoxanil was stronger in inhibiting the mycelium growth of the pathogen than mancozeb, but it was less effective in inhibiting the germination of sporangia and zoospores. Meanwhile these two fungicides were less effective in inhibiting mobility of zoospores. The mixtures of cymoxanil with mancozeb at the ratio of 1∶7 and 1∶8 were synergistic in inhibiting the germination of zoospores and mycelium growth, and synergistic ratio(SR) of the mixtures of the two compounds at the ratio of 1∶1~1∶10 was 1.55~5.39, and SR of the mixture of 1∶5 was as high as 5.39.