Abstract: Young panicles of rice (Oryza sativa L.) were treated with a range of concentration of EMS for 3 hours before cultured in vitro. The respiratory intensity of young panicleswas determined on the second, fourth, sixth day respectively, and the cytochrome oxidase activity and isoenzymes of cytochrome oxidase and malate dehyrogenase were analysed on the forth day. Tha experimental results show that the effects of EMS on respiratory intensity and activities of two enzymes of young panicles are in accordance with the effects of the mutagen on de-and re-differentiation of the young panicle cells. EMS affects metabolic processes in the cells at first and the induction rate of the young panicle callus changes consequently.