The purpose is to screen fungicides with good water solubility, environmental protection and strong bactericidal effect on plant pathogens. The bactericidal activity of pyridine-containing heterocyclic ammonium chloride cationic surfactants with different carbon chain lengths （C8, C10, C12, C14, C16） against four kinds of plant pathogens was tested by agar plate dilution method. The toxicity regression equation was obtained, and the effective antibacterial concentration （EC50） was calculated. The results show that the pyridine-containing heterocyclic ammonium chloride cationic surfactants with a carbon chain length of 12 （C12） has a significant antibacterial activity for Rhizoctonia solani Kühn, watermelon Fusarium wilt, apple valsa canker and Botrytis cinerea Pers. with the EC50 of 9.69×10 -3, 2.93×10 -2, 1.57×10 -5 and 1.85×10 -4g/L, respectively. While the EC50 of the control drugs containing jinggangmycin, methyl butazine, difenoconazole and mycoazole for the above plant pathogens individually are 7.02×10 -2, 0.506, 3.50×10 -4 and 2.04×10 -3 g/L, respectively. The EC50 value of C12 for four pathogens are significantly lower than the control drugs, which has good bactericidal activity and further research value. The minimal inhibitory concentration （MIC） of C12 against the four plant pathogens are 0.094, 0.091, 0.083 and 0.087 g/L, respectively. It provides the basis for the research on the prevention and treatment of plant pathogens by pyridine-containing heterocyclic ammonium chloride cationic surfactants.
