Both monotonic and cyclic shear strength of unsaturated soils are significantly affected by an initial effective stress condition and a degree of saturation. In this paper, we have studied influence of temperature change under closed condition on the shear behavior of unsaturated sandy soil experimentally. In addition, to consider the effects of solubility of gaseous component to the pore fluid, air and CO 2 are used as a gaseous material. The solubility of CO 2 into water is larger than ordinary air. Because the solubility of gaseous material varies with the temperature and the pressure, not only initial effective stress state but also the stress state during shearing process under closed condition are influenced. From the test results, it was found that the shear strength for the specimen subjected to temperature rise was smaller and that the shear strength for the specimen with CO 2 was smaller than that with air.