Ochratoxin A (OTA) is a highly toxic and carcinogenic mycotoxin whose toxicity includes hepatotoxicity, genotoxicity, cytotoxicity and immunotoxicity. Recently, there have been many studies on OTA biosynthetic gene clusters. AoOTAbZIP (also known as otaR1) basic region/leucine zipper (bZIP)-specific gene that controls the expression levels of 4 biosynthetic genes in the OTA biosynthetic pathway, bZIP gene is known to be involved in the regulation of mycotoxin biosynthesis by various environmental factors in eukaryotes. This study explored the regulation of OTA biosynthesis in Aspergillus ochraceus under AoOTAbZIP-mediated water activity stress. High water activity (0.96 AW) was beneficial to the growth of A. ochraceus, and moderate water activity conditions of 0.91 AW has a stress effect on A. ochraceus, among them the growth of the mutant strain was better than that of the wild type. The mutant did not produce OTA at any condition. Wild type toxin production and expression levels of the OTA biosynthetic genes decreased under both high water activity (0.96 AW) and moderate water activity (0.91 AW), indicating that the toxin production of A. ochraceus was also affected by this water activity degree, moreover, the expression levels of the biosynthetic genes in the mutant strain were inhibited to extremely low levels compared to the wild type. The pathogenicity experiments revealed that pears infected with WT and ΔAoOTAbZIP mutant strains showed no significant differences, indicating that the deletion of the AoOTAbZIP gene has no significant effect on the pathogenicity of A. ochraceus.