The weathering and oxidation of sulfides within mine tailings lead to acid drainage and release of heavy metals, which pollute ground water and surface water and damage ecological environment. Recent researches show that many factors can affect weathering of mine tailings. This paper points out that grain sizes, pH values and concentrations of organic matters in mine tailings can affect weathering and oxidation of sulfides. The qualitative observation and quantitative test of sulfides with optic microscope indicate that the rate of oxidation follows the sequence of PbS>ZnS>Fe1-x S>CuFeS2>FeS2 within sulfides of the same grain size. The experimental results also suggest that organic matters in mine tailings can prevent sulfide minerals from weathering and oxidation.