Resumo. The use of carbonized plant biomass has been recovered and evaluated as an alternative of improving soil fertility. The material generated, called biochar, is the product formed by pyrolysis, which is the thermal decomposition of biomass in a closed container under limited supply of oxygen and at relatively low temperatures. The chemical and structural composition of biochar is highly heterogeneous, with the exception of pH, which is usually higher than seven. Some properties are present in all kinds of biochar, including high carbon content and degree of aromaticity, which explains its high level of recalcitrance. However, its exact chemical composition and structure depends on the combination of raw material and pyrolysis conditions. When applied to soil, biochar can increase pH, cation exchange capacity and organic carbon and nutrient availability, raises in the abundance and functioning of mycorrhizal fungi, providing refuge for micro-organisms in the biochar micropores and improving soil structure and water availability. All these features in the soil interaction make its use in the agriculture normally to have positive effects on plant growth. It is believed that the use of biochar can contribute to carbon sequestration, it is considered by many as “carbon negative” due to its ability to promote plant growth and its stability in the soil. Studies with biochar have reached worldwide proportions involving different areas, and have grown a lot in recent years. However, there are still many uncertainties about its use in agriculture, mainly because the published papers have given more focus to biochar ability to maintain and improve soil fertility and increase agricultural productivity than to clarify the possible risks involved in biochar utilization.