To reveal the pathogenesis of Fusarium wilt in banana, the effects of Fusarium oxysporum f. sp. cubense race 4 (Foc4) on microorganism quantities and enzyme activities in the rhizosphere soil of potted banana (Musa AAA Cavendish subgroup cv. Baxi) were studied. The results showed that Foc4 had little effects on the total amount of microorganisms and the quantity of bacteria (B). But it significantly increased the quantity and percentage of the fungi(F) in the total microorganisms, decreased tho se of the actinomycete(A) and reduced the values of bacteria/fungi(B/F) and actinomycete/fungi(A/F). In addition, Foc4 significantly improved the activities of catalase and invertase. The findings revealed Foc4 infection affected the quantities of rhizosphere microorganisms, thus made the population structure unbalanced, which might be one of the main factors causing Fusarium wilt. That the activities of soil enzyme in banana rhizosphere changed significantly might be an important self-protection mechanism by improving the resistance of the rhizospheric microenvironment to fungi infection.