Abstract：Under the given condition of humidity of 60% and temperature of 25℃，two kinds of expansive soil are used for testing study on moisture content of standard absorption. One is mixed samples of kaolinite and montmorillonite in laboratory whose montmorillonite contents are 100%，50%，30%，20%，10% and 0，respectively，and another is expansive soil samples from three basins of Guangxi province，China. There is great difference between the moisture contents of standard absorption for soil from the tests of moisture absorption and dehydration. The physical definition of moisture content of standard absorption for soil from dehydration is clear and stable，so that 60% of moisture content of equilibrious absorption from dehydration is taken as the definition of moisture content of quasi-absorption. The moisture content of standard absorption for soil shows a linearity correlation with montmorillonite content，liquid limit，plasticity index and free expansive ratio of expansive soil，which reflects essential property of expansive soil，and is an important information to distinguish and classify expansive soils. The test method presented in this paper is simple and easy to run，so that the soil samples may basically arrive at stable state in 72 hours.
