A ¹⁴C-labelling technique was used to study turnover of microbial biomass C of 3 red soils with different texture, i. e., vegetable garden of red sandy soil, citrus orchard and tea garden of clayey soil, for which the turnover periods of soil microbial biomass C were 80 days, 139 days and 170 days, respectively. The turnover period was closely related to clay content, and longer in the red sandy soil than in the clayey soils, suggesting that organic matter can be faster decomposed and transformed by microorganisms and nutrients more easily released in the sandy soil, in other words, nutrients may be retained longer in clayey soil. However their turnover period was little affected by land use form, pH and organic matter content. In general, the turnover period for red soils was shorter than that reported for other types of soils, which shows that quicker turnover of organic matter and nutrients went on in acidic red soils of the tropical-subtropical regions and this may be one of the reasons for nutrient deficiency in red soils. To study the turnover of microbial biomass C is quite significant in evaluating and managing red soil fertility.