Abstract: The effects of pH and acid solvent on the antifungal activities of chitosan were studied by testing anthracnose, stem- end rot pathogens in Mango fruits and quiescent colletotrichum musae, crown rot pathogens in banana fruit. The results showed that pH4.8 and pH6.0 were both optimum to the antifungal activity of chitosan. The antifungal activery of chitosan was increased with the increase of its concentration. The activity of inhibition of chitosan in lactic acid was very strong for stem-rot pathogens, quiescent colletotrichum musae, and crown rot pathogens. The EC50 value increased as the tested pathogens increased, but they had some resistance reduced after the isolates were successively stimulated 40 times by application of chitosan. While the Botryodiplodiat heobromae Pat. exhibited the worst inhibition capability.

Key words: chitosan, mango, banana, panthracnose isolate, antifungal activity