Swelling deformation and swelling pressure tests of Tsukinuno bentonite and its mixtures with Toyoura sand were performed on a modified odometer. The swelling strain and swelling pressure of bentonite and its mixtures are dependent on the dry density, the increment of water content and the surface fractality of bentonite particle aggregates in voids. The water volume absorbed by bentonite is related to the surface fractal dimension (Ds) of bentonite. The correlation of the water volume to vertical overburden pressure (p) is obtained as Vw/Vm=KpDs 3 for Tsukinuno bentonite with fractal-textured surface. The maximum swelling strain is predicted according to the correlation of the water volume to vertical overburden pressure. The predictions of the maximum swelling strain are in satisfactory agreement with the experimental data. Furthermore, the good relationship between swelling strain and elapsed time is also proposed in this paper.