A novel glycoside hydrolases family 57 gene (gh-57) was found from a metagenomic fosmid library constructed from a black smoker chimney sample 4143-1 from the Mothra hydrothermal vent at the Juan de Fuca Ridge. Sequence and homology analysis using BLAST revealed that it had high similarity to gh-57 family. Conserved domain research revealed that the novel gh-57 contained a Glyco-hydro-57 domain and five conserved regions, including two putative catalytic residues Glu(154) and Asp(263). The three-dimensional features of the protein and its homologue from Pyrococcus horikoshii OT3 known as alpha-amylase were generated by homology modeling. The gh-57 gene was cloned, expressed, and purified in Escherichia coli using pQE system. Enzyme activity revealed that the recombinant protein could hydrolyze soluble starch and demonstrated amylase activity. It showed an optimal pH of 7.5, an optimal temperature of 90A degrees C, and its thermostability at 90A degrees C could remain over 50% enzyme activity for 4 h. The enzyme activity could be increased by DTT and Mg2+ while an inhibitory effect was observed with EDTA, ATP, and Ca2+. These results showed that the gh-57 gene was a novel thermostable amylase from oceanic microorganisms.