Protein-protein interactions (PPIs) play critical roles in the regulation of biological processes and the development of diseases. Our group found that THG-1 (TSC22 homologous gene-1) localized in the basal layer of normal squamous epithelium and overexpressed in squamous cell carcinomas. THG-1 is phosphorylated by the EGF-Ras-ERK pathway which is essential for promoting tumorigenesis. We also identified several THG-1 interacting proteins. Among them, Keap1 (Kelch-like ECH-associated protein1)-THG-1 interaction plays a crucial role in tumor progression. Therefore, inhibition of Keap1-THG-1 interaction is thought to be important for tumor suppression. In this study, we established a system to quantify the Keap1-THG-1 interaction using Nano-luc system, and performed drug repositioning screening of a chemical library from Univ. Tokyo. We identified several compounds as THG-1-Keap1 interaction inhibitor. Among these, a compound suppressed pNQO-1-ARE-luc and pHO-1-luc, suggesting that it suppresses the Nrf2 transcriptional activity. These results indicated that our screening system successfully screen the inhibitors of THG-1-Keap1 interaction. Further evaluation and large scale screening are required for future drug development.