Abstract: To analyze the cold tolerance differences in azalea cultivars of‘Elsie Lee’，‘Zi’e’and ‘Zihudie’，under natural low temperatures in Hangzhou（during Dec. 2013 to Mar. 2014），the relative leaf electric conductivities at seven sampling periods were determined and LT50 values were calculated using logistic equation. Moreover，some cold tolerance related physiological factors were measured，and through principal components analysis and correlation analysis，it was shown that the content of sucrose，soluble proteins，MDA and proline were closely related to cold tolerance in azalea. The accumulation of high level of sucrose as well as soluble proteins and proline played important roles in the cold tolerance in‘Elsie Lee’. Based on the data on the concent of MDA，it was suggested that the increase in contents of unsaturated fatty acid in lipid membrane may be another explanation for the stronger cold tolerance in ‘Elsie Lee’. Using subordinate function method to comprehensively evaluate the cold tolerance in three cultivars，it was found that‘Elsie Lee’ranked first and followed by‘Zihudie’and‘Zi’e’which had similar cold tolerance according to the data from tolerance evaluation by LT50 and SF method，and it can be concluded that the cold tolerance of‘Zihudie’is slightly stronger than‘Zi’e’based on their growth behaviors during winter seasons.

Key words: zalea, cold tolerance, physiological change, semi-lethal temperatures（LT50）, subordinate function（SF）method