The genome sequencing of Aspergillus oryzae completed in 2005 predicted eight genes of glutamate decarboxylase (GAD) isoforms. A detailed amino acid-sequence analysis of those GAD isoforms and gene expression study were performed. The homology of eight A. oryzae GAD isoforms was compared with those of other species. The isoforms could be divided into four groups based on identities of their amino acid sequences. Two of the isoforms had 31% homology with human GAD 65; two of the isoforms had 55 and 58% homology with rice GAD 1, respectively; two of the isoforms had 45 and 48% homology with yeast (Pichia stipites), respectively; two of the isoforms were unidentified. RT-PCR analysis showed that eight GAD genes were expressed in A. oryzae cultured in the rice solid medium, while four GAD genes were expressed in A. oryzae cultured in the yeast liquid medium. The presence of the eight genes for GAD isoforms in A. oryzae suggests that GADs must be utilized for specific purposes, which should be explored in future studies.