A gene(ST0817) encoding a putative thermophilic and acidic α-amylase from the thermophilic crenarchaeota Sulfolobus tokodaii strain 7 was cloned and functionally overexpressed in Escherichia coli.The recombinant enzyme was purified to homogeneity after heat treatment,Ni-NTA affinity and superdex-200 gel filtration.The relative molecular mass of α-amylase was 53.0 kDa on SDS-PAGE.The purified enzyme displayed optimal activity at 70°C and pH 5.5.It had a half-life of 8 h at 85°C.The enzyme was found to have high pH stability and maintained about 50% of activity even after 120 min of treatment at pH 5.2.The enzymatic activities of the purified enzyme towards different substrates were listed from high to low as follows: amylose > soluble starch > amylopectin > β-cyclodextrin > glycogen > cyclodextrin > pullulan.The enzyme was found to have high tolerance to organic solvents,metal ions and detergents.