Premature leaf senescence affects plant yield and quality, and numerous researchesabout it have been conducted until now. In this study, we identified an early senescentmutant es4 in rice (Oryza sativa L.); early senescence appeared approximately at 60 dps and became increasingly senescent with the growth of es4 mutant. We detected thatcontent of reactive oxygen species (ROS) and malondialdehyde (MDA), as well as activityof superoxide dismutase (SOD) were elevated, while chlorophyll content, soluble proteincontent, activity of catalase (CAT), activity of peroxidase (POD) and photosynthetic ratewere reduced in the es4 mutant leaves. We mapped es4 in a 33.5 Kb physical distanceon chromosome 4 by map-based cloning. Sequencing analysis in target intervalindicated there was an eight bases deletion mutation in OsCPK12 which encodeda calcium-dependent protein kinase. Functional complementation of OsCPK12 ines4 completely restored the normal phenotype. We used CRISPR/Cas9 for targeteddisruption of OsCPK12 in ZH8015 and all the mutants exhibited the prematuresenescence. All the results indicated that the phenotype of es4 was caused by themutation of OsCPK12. Overexpression of OsCPK12 in ZH8015 enhanced the netphotosynthetic rate (Pn) and chlorophyll content. OsCPK12 was mainly expressed ingreen organs. The results of qRT-PCR analysis showed that the expression levels ofsome key genes involved in senescence, chlorophyll biosynthesis, and photosynthesiswere significantly altered in the es4 mutant. Our results demonstrate that the mutantof OsCPK12 triggers the premature leaf senescence; however, the overexpression ofOsCPK12 may delay its growth period and provide the potentially positive effect onproductivity in rice.