Scales of silver carp(Hypophthalmichthys molitrix)were collected in winter and summer.Acid-soluble collagens(ASC)were extracted from the scales collected from the two seasons,respectively.Thermal stability of the collagens was investigated by changes in circular dichroism(CD)spectrum upon heating.The CD measurement results showed different thermostability of winter and summer samples heated at 30,33 and 35℃.The melting temperature of scale ASC from summer fish was 36 ℃,while scale ASC from winter fish showed the existence of biphasic thermal transitions with the melting temperature of 30 and 34 ℃.It was concluded scale ASC from the summer group was more stable than its equivalent from the winter season.The difference might be the consequence of the need to adapt to the habitating environment.