The turnover of the microbial biomass plays key roles in the cycling of organic matter and nutrients in soil.Although the microbial biomass-C is generally accounted for only 1%~4% of total soil organic, the balance between the rate of microbial processes determines the turnover and consequently the accumulation of soil organic matter and nutrients (e g.N, P and S).In this study, the procedure for measuring the turnover time of soil microbial biomass-C has been developed.¹⁴C-labelled glucose was used to label the biomass-C by incubating soils at 25 and 100% humidity.The labelled biomass-C, total biomass-C, and extractable-C were measured by every 20 days during a 100-day incubation period, using the fumigation-extraction method.Data obtained were then used to calculate the turnover rate constant of biomass-C, and hence its turnover time Under the incubation condit ions, the turnover t ime of biomass-C, calculated from the gross turnover rate constant of labelled biomass-C, varied between 93 and 400 days.This is equivalent, by extrapolation, to 1.0~4.1 years under the field conditions where soils were from.It was demonstrated that the turnover time of soil biomass- C was largely affected by soil texture but little by management.Measuring the turnover times of soil biomass-C provides a good indication of microbial activities in relating to the turnover and accumulation of soil organic matter.