The synthesis of acid protease in rice-koji is important for sake brewing. Northern blot analysis was carried out to study the transcriptional regulation of acid protease-en coding gene (pepA) in Aspergillus oryzae. The pepA gene was not expressed in submerged culture, while it was expressed when cultured on steamed rice. Additionally, the culture at high temperature (>38degreesC caused a marked decrease in transcription level of pepA, although the a-amylase (amyB) and actin genes were expressed regardless of the temperature. To examine whether the pepA promoter controlled the temperature-dependent expression, the promoter regions of pepA and amyB were introduced into a vector containing the GUS reporter gene (uidA gene). Northern blot analysis showed that the elevation of culture temperature caused the loss of uidA expression in the pepA promoter-uidA transformant but not in the amyB promoter-uidA transformant. These results suggest that its promoter controlled the temperature-dependent expression of pepA.