MORF-RELATED GENE702 (OsMRG702) regulates flowering time genes in rice, but how it controls transcription is not well known. Here, we found that OsMRGBP can directly interact with OsMRG702. BothOsmrg702andOsmrgbpmutants show the delayed flowering phenotype with the reduction in the transcription of multiple key flowering time genes, includingEhd1andRFT1. Chromatin immunoprecipitation study showed that both OsMRG702 and OsMRGBP bind to theEhd1andRFT1loci and the absence of either OsMRG702 or OsMRGBP leads to a decrease of H4K5 acetylation at these loci, indicating OsMRG702 and OsMRGBP cooperatively together to promote the H4K5 acetylation. In addition, whilstGhd7are upregulated in bothOsmrg702andOsmrgbpmutants, only OsMRG702 binds to the loci, together with the global increased andGhd7locus-specific increased H4K5ac levels inOsmrg702mutants, suggesting an additional negative effect of OsMRG702 on H4K5 acetylation. In summary, OsMRG702 controls flowering gene regulation by altering H4 acetylation in rice; it works either together with OsMRGBP to enhance transcription by promoting H4 acetylation or with other unknown mechanisms to dampen transcription by preventing H4 acetylation.