【Objective】The stability of biochar provides a basis for a better understanding of its potential to sequestrate soil carbon(C). This study aimed to study the stability of rice straw biochar in a Zelkova serrata plantation soil under in situ conditions and to explore the relationship between the stability of biochar, its chemical properties, soil temperature, and soil moisture content.【Method】Two biochars were produced by pyrolyzing rice straw at 300 ℃ and 500 ℃. By using ¹³C isotope, the stability of the biochars in soils was examined through 182 d in situ experiments in a Zelkova serrata plantation.【Result】The cumulative decomposition of 300 ℃ and 500 ℃ biochars was 10.5 and 3.65 g·m^–2, respectively, during the entire experiment. The results of double-exponential fitting indicated that the mean residence time of the recalcitrant C in 300 ℃ and 500 ℃ biochars were 99.8 a and 302 a, respectively. The decomposition rate of 300 ℃ biochar was significantly positively correlated with surface soil temperature(P = 0.034, r = 0.417, n = 26)but not for 500 ℃ biochar(P = 0.549, r = 0.123, n = 26). This indicated that the effect of soil temperature on biochar stability depends on its pyrolysis temperature.【Conclusion】To sum up, this study demonstrated that biochar produced at 500 ℃ is more stable than biochar produced at 300 ℃ through in situ experiments, and provides basic data for further study on biochar stability.