Biomass-derived black carbon, also cited as biochar, refers to the highly aromatic infused solid material produced by plant biomass pyrolysis and carbonization under oxygen-limited conditions. Biochar represents a large portion of the global carbon that may have served as a carbon sink over geological time scales. However, whether biochar can become one of the important materials for human being to tackle with future climate change is mainly depended on its biological and chemical stability in soil ecosystem. Therefore, it is of great importance to clarify the biotic and abiotic stability of biochar in soil ecosystem so that the role biochar may have played in past climate change or how it can be used to mitigate future climate change could be better understood. Results of the studies will be essential for scientific assessment and valuation of biochar's role in carbon sequestration and emission mitigation in soil ecosystem. Although biochar has generally been regarded as biologically and chemically recalcitrant, many studies have shown its oxidation in the environment. In this review, biotic and abiotic oxidation characteristics of biochar in soil ecosystem have been summarized. Abiotic oxidation of biochar, which has been observed to form O-containing functional groups on the surface, mainly occurs by chemical oxidation, photo-oxidation and inorganic cracking. In contrast, biotic oxidation of biochar takes place through two processes, namely that microbes utilized biochar directly as a carbon source or indirectly through co-metabolism. In addition, effects of biochar properties and environmental conditions on the biochar stability have also been discussed. Raw materials, pyrolysis processes and pyrolysis conditions, which control the physiochemical characteristics of biochar, play a significant role in its stability. On the other hand, while incorporating into soil, it has been discovered that stability of biochar could be significantly influenced by soil conditions, such as soil pH, water regimes and soil aggregate etc. Recent studies also indicated that climate conditions might have great impacts on the biochar stability. Therefore, attention needs to be paid about the combined influences of climate and soil conditions on the biotic and abiotic stability of biochar in the future. Up to now, modeling is the best method in predicting long-term stability of biochar. Recent studies have shown that degradation model of biochar could be established based on its easily obtainable characteristics. Characteristics of biochar, such as volatile matter, O : C molar ratio, the initial proportion of nonaromatic C, degree of aromatic C condensation and a new recalcitrance index, the R₅₀, which all reveal physiochemical structure differences between biochars, could be considered as appropriate screening tools for the stability of biochar. On the other hand, in order to predict biochar decomposition in soil ecosystem, experimentally based degradation rate models, such as the first order dynamic model and double-exponential model, are commonly utilized. Nevertheless, some disadvantages of the models have been found due to short-term experiment and take few soil properties into account. Therefore, long-term field experiments must be conducted in order to develop a more accurate scientific model for predicting the biochar stability in soil ecosystem. Meanwhile, simulation experiment with different types of soil and crop plantation patterns are urgently needed to precisely model the long-term stability of biochar in various agricultural ecosystems.