Abstract: Ant nesting can modify soil physicochemical conditions in the tropical forest, exerting a crucial effect on spatiotemporal variation in soil microbial biomass carbon and quotient. In this study, the chloroform fumigation method was used to measure the spatiotemporal dynamics of microbial biomass carbon and quotient in ant nests and the reference soils in Syzygium oblatum community of tropical Xishuangbanna. The results were as following: 1) Microbial biomass carbon and quotient were significantly higher in ant nests (1.95 g·kg^-1, 6.8%) than in the reference soils (1.76 g·kg^-1, 5.1%). The microbial biomass carbon in ant nests and the reference soils showed a signifi-cantly unimodal temporal variation, whereas the temporal dynamics of microbial biomass quotient presented a distribution pattern of “V” type. 2) The microbial biomass carbon and quotient showed significant vertical changes in ant nests and the reference soils. The microbial biomass carbon decreased, and microbial biomass quotient increased significantly along the soil layers. The vertical variations in microbial biomass carbon and quotient were more significant in ant nests than in refe-rence soils. 3) Ant nesting significantly changed the spatiotemporal distributions of soil water and temperature in ant nests, which in turn affected spatiotemporal dynamics of soil microbial biomass carbon and quotient. Soil water content could explain 66%-83% and 54%-69% of the variation of soil microbial biomass carbon and quotient, respectively. Soil temperature could explain 71%-86% and 67%-76% of the variation of soil microbial biomass carbon and quotient in ant nests and the reference soils, respectively. 4) Changes in soil physicochemical properties induced by ant nesting had significant effect on the soil microbial biomass carbon and quotient. There were positive correlations of soil microbial biomass carbon to soil organic carbon, soil temperature, total nitrogen and soil water content, and to bulk density, nitrate nitrogen and hydrolyzed nitrogen; whereas a negative correlation of them was observed with soil pH. Soil pH was positively and other soil physicochemical properties were negatively correlated with microbial biomass quotient. Total organic carbon, total nitrogen and soil temperature had greater contribution to microbial biomass carbon, while total organic carbon and total nitrogen had the least negative effect on microbial biomass quotient. Therefore, ant nesting could modify microhabitats (e.g., soil water and soil temperature) and soil physicochemical properties (e.g., total organic carbon and total nitrogen), thereby regulating the spatiotemporal variation in soil microbial biomass carbon and quotient in tropical forests.