Response of physiological and biochemical indexes in leaves of four Lolium perenne varieties was compared under simulated drought stress using different concentrations of PEG solution. "Oupec", with the highest relative water content and least decreasing changes, the lowest electrical conductivities,and the smallest increasing rates of MDA contents under PEG stress had more tolerant membrane systems and was the most resistant to osmotic stress, while the resistance of "Polim" was relatively weaker. Proline accumulation in leaves of the four varieties increased and "Oupec" with rapid increases in proline contents had the strongest resistance to PEG stress. Activities of superoxide dismutase (SOD) in leaves of the four varieties increased during the initial stress stages (5% PEG) and decreased continuously with more severe stress. "Oupec" and "Polim" had the strongest and the weakest drought resistance respectively. The four L. perenne varieties had reduced relative water contents and activities of superoxide dismutase (SOD), increased permeability of plasma, MDA contents and proline accumulation under PEG stress and had differences in rates of change for the response indices.