Objective: The motivation of this study was to investigate the effect of grape seed extract on dentin remineralization. Methodology: Sound dentin disks were prepared from the buccal surfaces of human impacted third molars. The specimens were stored in demineralizing solution for 72 hours at room temperature to create artificial carious lesions. They were divided into four groups according to the treatment used; 15% GSE, 1000 ppm sodium fluoride, artificial saliva meanwhile teeth in the fourth group were kept without treatment as a negative control group. An in vitro pH cycling model for eight successive days was done. Subsequently micro-hardness of the specimens and their micro-morphological appearance were evaluated using micro-indenter and Environmental scanning electron microscope (ESEM) respectively. Data were statically analyzed. Results: The results indicated that there was a significant increase in dentin micro-hardness values of GSE and NaF groups in comparison to the demineralized and artificial saliva groups. The ESEM micrographs confirmed the micro-hardness results. Conclusions: GSE is a promising natural remineralizing agent for treatment of the demineralized dentin.