In order to define the effect of straw-mulching on population number of bacteria in wheat fields and the relationship between straw-mulching and wheat sharp eye-spot, variation of population of bacteria was analysed with the dilution plate counting method and incidence of wheat sharp eye-spot investigated. Results showed that the total number of bacteria and fluorescent pseudomonads was much higher in straw-mulched plots than in not -mulched. The effect of straw-mulching on total number of bacteria and fluorescent pseudomonads was greater in the earlier stage than in the later stage. No significant difference was found in the proportion of antagnistical bacteia between straw-mulched and not-mulched fields. More than 90% of the fluorescent pseudomonad strains were antagonistic to Rhizoctonia cerealis. The incidence of wheat sharp eye-spot in straw-mulched fields was lower than in not-mulched.