To elucidate the adsorption sites and behavior of Sr atoms on smectite, EXAFS spectroscopy was performed at the Spring-8 using air-dried and wet-paste samples of Sr-adsorbed bentonite adjusted to pH 4.7 and 9.6. EXAFS analyses were conducted for the two-oxygen shell fit using a crystalline SrSO₄ as a reference compound. The first-neighbor shells consisted of 5.5 0 atoms of water molecules at a distance of 2.58 Å in the air-dried sample and 7.0 0 at 2.60 Å in the wet sample. The second shells consisted of 2.6 0 atoms at a distance of 2.77 Å and 2.5 0 at 2.81 Å for the air-dried and wet samples, respectively. Only the Debye-Waller factors of the second shells were affected by the pH, resulting to be smaller at pH 4.7 than those observed at pH 9.6. It is concluded from the EXAFS results that Sr atoms are attracted stronger to the 2: 1 sheets of smectite in the air-dried compacted samples than in the wet-paste samples because of the smaller Debye-Waller factors in the air-dried compacted samples. The Sr atoms hovered on a triangle of the oxygen hexagonal cavity on the flat surface of 2: 1 sheets and resided on the broken face of the octahedral sheets at the edge surface. In addition, they behaved as hydrated ions and formed incomplete outer-sphere complexes at high water content; however, they formed incomplete inner-sphere-like complexes together with oxygen atoms of the 2: 1 sheets in the air-dried samples. The Sr atoms also played a role combining two sheets of the 2: 1 layer of smectite in forming the edge-toedge and edge-to-face associations.