In an attempt to link the microbial community composition and function in mine tailings to the generation of acid mine drainage, we simultaneously explored the geochemistry and microbiology of six tailings collected from a lead/zinc mine, i.e. primary tailings (T1), slightly acidic tailings (T2), extremely acidic tailings (T3, T4 and T5) and orange-coloured oxidized tailings (T6). Geochemical results showed that the six tailings (from T1 to T6) likely represented sequential stages of the acidification process of the mine tailings. 16S rRNA pyrosequencing revealed a contrasting microbial composition between the six tailings:Proteobacteria-related sequences dominated T1–T3 with relative abundance ranging from 56 to 93%, whereasFerroplasma-related sequences dominated T4–T6 with relative abundance ranging from 28 to 58%. Furthermore, metagenomic analysis of the microbial communities of T2 and T6 indicated that the genes encoding key enzymes for microbial carbon fixation, nitrogen fixation and sulfur oxidation in T2 were largely fromThiobacillus and Acidithiobacillus, Methylococcus capsulatus, and Thiobacillus denitrificansrespectively; while those in T6 were mostly identified inAcidithiobacillus and Leptospirillum, Acidithiobacillus and Leptospirillum, and Acidithiobacillusrespectively. The microbial communities in T2 and T6 harboured more genes suggesting diverse metabolic capacities for sulfur oxidation/heavy metal detoxification and tolerating low pH respectively.