The majority of peach cultivars which cultivated on Mashhad climatic condition were damaged on winter of 2008 due to -22 centigrade degree. Only a few cultivars do well. The key to successfully growing peaches is choosing the right cultivars. Frost tolerance and winter die-back of bud flowers of 5 peach cultivars (‘G. H. Hill’, ‘Alberta’, ‘Redhaven’, ‘Amsden’ and the local cultivar ‘Sorkhosefid Mashhad’) during January and February of 2009 were determined. Shoots collected from adult trees in the orchard and submitted to different temperatures in artificial freezing from -10 to -30 centigrade degree, employing a cooling rate of 2oC h-1. Bud flowers were visual tested in addition TTC and electrolyte leakage methods and evaluated in terms of their suitability for use in detecting damage to sigma, ovary and stamen parts of flowers. The average lethal temperature of 50% of the flower buds (LT50) was determined for each cultivar which was between -24 and -26oC in the January. Among examined cultivars ‘Redhaven’ was the most sensitive to low temperatures, which LT50 accrued on -24 and LT80 on -26 centigrade degree, while The buds of cv. ‘G. H. Hill’ showed a greater frost resistance with LT50 of -26 and LT80 of -30 centigrade degree. The effect of examination time was highly significant. In January and February due to the mild weather in February, the frost tolerance of flower buds decreased rapidly

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