Abstract: Effect of pH on the sorption distribution coefficient (K_d) and apparent diffusion coefficient (D_a) of ~(152,154)Eu(Ⅲ) in the compacted bentonite is studied with the capillary method. The diffusion profiles at different pH values fit the Fick’s second law very well and the values of K_d are in good agreement with the literature data under similar experimental conditions. The results show that the apparent diffusion coefficient of ~152,154Eu(Ⅲ) in the compacted bentonite decreases with increasing pH and the sorption distribution coefficient of ~(152,154)Eu(Ⅲ) increases with increasing pH, and the sorption distribution coefficient of Eu(Ⅲ) decreases with increasing the compacted bentonite bulk density. Evidently, the effects of pH and bulk density of compacted bentonite are sufficient importance to merit consideration in the assessment of the bentonite as an engineering barrier.