Abstract: Seedlings of hybrid rice(Oryza sativa subsp. indica cv, Weiyou 287, Shanyou 287, Shanyou 63)were osmotic stress with polyethyleneglycol (PEG₄₀₀₀). The water content and relative water content of the rice seedlings were gradually decreased under osmotic stress(-0.95MPa), content of free proline and malondialdehyde(MDA)and permeability of plasma membrane increased sharply; however, there was a positive correlation of content of free proline with the level of membrane-lipid peroxidation. The response of the different hybrid rice combinations to osmotic stress was different. The index of unsaturated fatty acid (IUFA)in membrane lipids decreased treated by PEG.There was a negative relation between IUFAand content of free proline under osmotic stress.