Objective: In this study, the time-related pH changes that occur in cements having different structures were observed. Method and materials: Eight cements consisting of four permanent and four temporary cements were used. The materials were prepared according to manufacturers' instructions. The materials were used in 0.100 +/- 0.02-g increments, with the purpose of standardizing the effect of massive differences. The 80 total specimens, including 10 from each cement type, were prepared, and the pH value of the distilled water was measured at 3, 10, 30, 60, and 120 minutes, and then again 24 hours later. Results: Analysis of variance showed the relation between the kind of cement and its pH change during the course of the study was statistically significant. Conclusion: Though temporary cements indicated neutral pH from the beginning of the study, the acidity of the other cements changed with time and took values approximate to neutral pH within 24 hours.