The antibacterial activity of chitosans with three different molecular weight on the six strains of Fusarium oxysporum f.sp.cubense was described.It was revealed that the chitosans inhibited the activity of Fusarium oxysporum f.sp.cubense in a certain range,and had an effect on the Fusarium oxysporum f.sp.cubense colony morphology,hypha growth and spore germination.The antibacterial effect with higher molecular weight chitosans was superior to the effect of the lower molecular weight.The effect of antibacterial activity of C-290k was higher than others,the effect of antibacterial activity of R1-248 was 90.27% at the concentration of 1 000 mg/L.