Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important regulator of the maturation and function of cells in the granulocyte and macrophage lineages, and also plays a significant role in wound healing. In a previous study, we expressed human GM-CSF in rice cells (rice cell-derived human GM-CSF; rhGM-CSF). The purpose of the present study was to evaluate its effect on wound healing in oral mucositis.