This study evaluated the efficacy of fine Surface Prereacted Glass-ionomer (S-PRG) powder as a medicament for dentin hypersensitivity. Bovine dentin specimens with simulated hypersensitive surfaces were constructed through 10% phosphoric acid etching and hydroxyapatite paste abrasion. The surfaces of these abraded specimens were scrubbed with the fine S-PRG powder (S-PRG group). For the comparison, others were treated with a powder of glass-ionomer cement: fluoroaluminosilicate glass powder (FAS group). An untreated group was prepared as a control. Before and after immersion in demineralizing solution, surface textures and the occlusion of dentinal tubules were observed and assessed by SEM. After demineralization, EPMA analyses were also carried out to detect elements on the treated and fractured dentin surfaces. Mineral contentprofiles of the lesions and the total amount of mineral removed, expressed as Integrated Mineral Loss (IML), were obtained by transversal microradiography in order to measure the effect of treatment of the underlying dentin, against demineralization. SEM observations revealed that the dentin surfaces of the S-PRG group were covered with powder and the dentinal tubules were completely occluded with fine particles, even after demineralization. On the contrary, dentinal tubules of the FAS group were only partially occluded, and there was no powder residue in evidence at all after demineralization. EPMA analysis showed that deposits of calcium, fluoride and aluminum were detected to a higher degree in the S-PRG group in comparison with the FAS group. Calcium was characteristically detected at the orifice of dentinal tubules, which is indicative of the anti-demineralizing effect of the fine S-PRG powder. The mineral profiles of the S-PRG and the FAS groups were different from that of the control group; in particular, the S-PRG group showed distinct surface layers with a thick and high % volume of minerals. The S-PRG group also indicated a significantly lower IML compared with the control and FAS groups (p<0.05). These results suggest that fine S-PRG powder will have a superior, occluding effect on opened dentinal tubules and will provide acid resistance to the underlying dentin. Fluoride and other minerals in concentrated release from S-PRG powder may contribute to remineralization in the tubules, and occlusion, over a long period. These characteristics lent much weight to the premise that the application of fine S-PRG powder is an effective medicament for dentin hypersensitivity.