The C-terminal domain of Aspergillus oryzae glucoamylase was analyzed by site-directed mutagenesis using glucoamylase cDNA. A mutant glucoamylase cDNA lacking the region corresponding to the C-termlnal domain of the wild-type glucoamylase was constructed by inserting two stop codons in the gene for the wild-type glucoamylase. The wild-type and mutant glucoamylase cDNAs were expressed in Saccharomyces cerevisiae YPH 250, and then the produced wild-type and mutant glucoamylases were purified by acarbose affinity column chromatography. As compared to those of the wild-type glucoamylase, the K-m values of the mutant enzyme determined using maltose, maltotriose or maltopentaose as a substrate were similar, but that determined using soluble starch as a substrate was twofold higher. The mutant glucoamylase showed a low rate of hydrolysis of raw cornstarch, although the wild-type glucoamylase showed a high rate of raw cornstarch hydrolysis. These results indicated that the C-terminal domain is important in the affinity of the enzyme to raw starch as reported for the glucoamylase of Aspergillus awamori.