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JAZ proteins function as transcriptional regulators that form a jasmonic acid–isoleucine (JA-Ile) receptor complex with coronatine insensitive 1 (COI1) and regulate plant growth and development. These proteins also act as key mediators in signal transduction pathways that activate the defense-related genes. Herein, the role of <i>OsJAZ4</i> in rice blast resistance, a severe disease, was examined. The mutation of <i>OsJAZ4</i> revealed its significance in <i>Magnaporthe oryzae</i> (<i>M. oryzae</i>) resistance and the seed setting rate in rice. In addition, weaker <i>M. oryzae</i>-induced ROS production and expression of the defense genes <i>OsO4g10010</i>, <i>OsWRKY45</i>, <i>OsNAC4</i>, and <i>OsPR3</i> was observed in <i>osjaz4</i> compared to Nipponbare (NPB); also, the jasmonic acid (JA) and gibberellin4 (GA4) content was significantly lower in <i>osjaz4</i> than in NPB. Moreover, <i>osjaz4</i> exhibited a phenotype featuring a reduced seed setting rate. These observations highlight the involvement of <i>OsJAZ4</i> in the regulation of JA and GA4 content, playing a positive role in regulating the rice blast resistance and seed setting rate.