Abstract: It has become a common understanding that freezing-thawing cycling is a kind of weathering process which considerably changes the engineering properties of soils due to cryogenic actions.Freezing-thawing induced changes in strength of two overconsolidated soils were studied.The soil samples were subjected to one freezing-thawing cycle.Then the mechanical test and SEM micro-fabric scanning were carried out on both pre-freezing and post-thawing samples.It was found that the strength parameters of the two soils changed in an opposite way.Novel explanations on the mechanism of the changes were given by using SEM quantitative analysis and according to the deforming process during freezing-thawing.