Differential scanning calorimetry（ DSC） was used to measure the thermal hysteresis activity(THA) of plant antifreeze proteins(AFPs). The results reveal that DSC is a good method to screen and study AFPs. In the sixteen components extracted from Ammopipanthus mongolicus leaves, one(P3S1) was found to have apparent thermal hysteresis activity by DSC. As the amount of ice nuclei in the sample decreased, the THA of P3S1 increased from 0.01℃ to 0.65℃ . It is notable that the two- peak thermal hysteresis effect was observed. Two endothermic peaks appeared in the melting process of P3S1, while the freezing peak also consisted of two peaks. The peaks appeared antecedently showed larger thermal effect. This phenomenon shows P3S1 has two different kinds of interaction with water and ice crystal. It is probably an important property of a class of AFPs.
