The aim of this study was to investigate the cellular effects of Portland cement on cultured human pulp cells. Using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, no cytotoxicity was observed in the Portland cement group in comparison with the negative control group, whereas the glass ionomer cement, intermediate restorative material, and Dycal groups showed a survival rate of less than 40% at 12 hours. Scanning electron microscopy revealed that human pulp cells attached to the Portland cement were flat and had numerous cytoplasmic extensions. In the groups in which other materials were used, a few rounded cells were observed on the material but no living cells were observed. The expression of both osteonectin and dentin sialophosphoprotein mRNAs was induced in the Portland cement-treated group. These results suggest that Portland cement is biocompatible, allows the expression of mineralization-related genes on cultured human pulp cells, and has the potential to be used as a proper pulp-capping material.