Cyanobacteria are ancient photosynthetic prokar-yotes that have adapted successful y to adverse environments including high‐light irradiation. Although it is known that the repair of photodamaged photosystem II (PSII) in the organisms is a highly regulated process, our knowledge of the molecular components that regulate each step of the process is limited. We have previously identified a hypothetical protein Slr0151 in the membrane fractions of cyanobacterium Synechocystis sp. PCC 6803. Here, we report that Slr0151 is involved in PSII repair of the organism. We generated a mutant strain (Dslr0151) lacking the protein Slr0151 and analyzed its characteristics under normal and high‐light conditions. Targeted deletion of slr0151 resulted in decreased PSII activity in Synechocystis. Moreover, the mutant exhibited increased photoinhibition due to impairment of PSII repair under high‐light condition. Further analysis using in vivo radioactive labeling and 2‐D blue native/sodium dodecylsulfate polyacrylamide gel electrophoresis indicated that the PSII repair cycle was hindered at the levels of D1 synthesis and disassembly and/or assembly of PSII in the mutant. Protein interaction assays demonstrated that Slr0151 interacts with D1 and CP43 proteins. Taken together, these results indicate that Slr0151 plays an important role in regulating PSII repair in the organism under high‐light stress condition.