The crystal structure of Taka-amylase A has been determined by a combination of multiple isomorphous and molecular replacement methods to 3 .0 A resolution. A model of the protein has been completed with the aid of the amino acid sequence. The molecule consists of two globular domains, main and C-terminal ones which are connected by only one peptide chain. The main domain has an eight-fold α/β barrel and the C-terminal domain is made up of an eight -stranded β/β structure. The carbohydrate is located at the molecular surface on the opposite side of the active cleft. The essential Ca2+ was found to be buried in the molecule nearr the catalytic site.The binding mode of the substrate and the catalytic mechanism were examined briefly.