Spring freeze events seriously limit the growth, development, and grain yield of winter wheat (Triticum aestivum L.). A 2-yr eld experiment with two contrasting cultivars: XM21 (low-temperature resistant) and XZ24 (low-temperature sensitive), was conducted using an air temperature control device designed to allow investigation of the physiological and grain yield responses to spring freeze. e plants were grown in the eld and subjected to a 5-d spring freeze episode (approximately 8°C lower than the ambient temperature) at jointing stage (Zadoks scale 31). Spring freeze signi cantly decreased gas exchange rates and maximum quantum e ciency of photosystem II in wheat leaves of both cultivars. Under spring freeze, the yield loss was 12 to 14% in XZ24 vs. 5 to 6% in XM21. Greater yield loss in XZ24 coincided with a greater reduction of tiller and spike number in XZ24 than in XM21. Spring freeze occurring at jointing stage depressed the photosynthetic capacity of the leaves when measured at the end of the 5-d period and again at 7 d later, resulting in lowered number of e ective tillers, and eventually decreasing the grain yield. e genetic and/or bio-physiochemical basis for the di erent sensitivity of tiller development to spring freeze between the two cultivars could be further exploited for breeding new wheat cultivars tolerant to spring freeze stress.