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Lesion mimic mutants are excellent models for research on molecular mechanisms of cell death and defense responses in rice. We identified a new rice lesion mimic mutant <i>lmm24</i> from a mutant pool of <i>indica</i> rice cultivar &#8220;ZhongHui8015&#8221;. The <i>LMM24</i> gene was identified by MutMap, and <i>LMM24</i> was confirmed as a receptor-like cytoplasmic kinase 109 by amino acid sequence analysis. The <i>lmm24</i> mutant displayed dark brown lesions in leaves and growth retardation that were not observed in wild-type ZH8015. The results of histochemical staining and TUNEL assays showed enhanced ROS accumulation and cell death in <i>lmm24</i>. Chloroplast degradation was observed in <i>lmm24</i> leaves, with decreased expression of photosynthesis-related genes and increased expression of the senescence-induced <i>STAYGREEN</i> (<i>SGR</i>) gene and other senescence-associated genes. Furthermore, <i>lmm24</i> exhibited enhanced resistance to rice blast fungus <i>Magnaporthe oryzae</i> (<i>M. oryzae</i>) and up-regulation of defense response genes. Our data demonstrate that <i>LMM24</i> regulates cell death and defense responses in rice.