Abstract:Dry or germinated seeds from hybrid rice "Youza" and its parents"Qiguizao' and u Lemont" were treated by 5-10 μmol/L of methyl viologen(MV) for 24 hours. Seed vigor and seedling growth were inhibited pronouncedly butgermination rate was not disturbed. The ratio of coleoptile/radicle length increased by 1.4- to11.0-fold over the control because the depression of radicle growth was more serious thanthat of plumule. Tissue electrolyte leakage was enhanced and subsequent greening did notoccur, then seedlings were dead in the following few days．MV treatment with leaf segments or roots of intact rice seedlings at 3-leaf stage caused membrane leakage， chlorophyll degradation，the decline of photosynthesis and the increase of dark respiration．The response of hybrid rice Youza to MV was slightly less susceptible than its parents． The results suggest that MV can enter the different organs of rice and display its toxicity．MV seems to induce not only the oxidative degradation of chlorophyll but also the limitation of chlorophyll formation．