Abstract: Rice seeds were sown in soils treated with different calcium_containing chemicals. Calcium oxide had a distinct physiological effect on rice seedlings . In comparison with the control, the height of shoot, the number of roots and leaves all increased at the the application of 1.0% of CaO. Further studies indicated that the soil with 0.5%～1.5% CaO added reduced the leakage of electrolytes and the content of malonaldehyde, increased the content of chlorophyll and soluble protein in seedlings under chilling stress. The enhanced activity of peroxidase may be the cause of CaO improving the cold_tolerance of rice seedlings.