To elucidate the features of active organic carbon in Karst soils in the turnover of soil organic carbon, 14C–labeled straw and 14C–labeled calcium carbonate were respectively added to each of the terra fusca, rendzina and zonal red soil of Huanjiang Guangxi for a 100 d incubation test. Soils with no addition were regarded as CK. Results showed that 14C–labeled straw exhibited obviously higher influence on 14C–MBC, 14C–DOC in the three soils, compared to 14C–labeled calcium carbonate (P<0.05). After 5 d of incubation, total MBC (microbial biomass carbon) reached the peak in the three soils added with 14C–labeled straw or 14C–labeled calcium carbonate, and the MBC in red soils was 231.7，273.0 mg/kg , were respectively 70.2% and 100.5% higher than that in the CK ; the MBC in terra fusca was 288.1, 307.7 mg/kg , were respectively 23.0% and 31.3% higher than that in the CK while MBC in rendzina was 683.7，787.2 mg/kg , were respectively 4.5% and 20.3% higher than that in the CK; DOC (dissolved organic carbon) in the three soils also reached the maximum. The MBC in rendzina was obviously higher than that in terra fusca and red soil, but the DOC in red soil was obviously higher in terra fusca, rendzina (P<0.05). Exogenous 14C–labeled matters could promote the increase of soil active organic carbon and in the same condition, rendzina and terra fusca are more likely to accumulate organic carbon, compared to red soil.