Objectives: To examine the cytotoxic effects of MTA and Ca(OH)2 on 3T3 fibroblasts at different time intervals. Methods: Confluent cells were cultured with Ca(OH)2 and MTA in six-well plates. Wells with only fibroblasts served as controls. Cell number and viability were determined after 24 and 48 hours and 7 days of incubation. For cell viability, trypane blue exclusion assay was used. A Leitz inverted microscope was used to observe the morphologic behavior of cells. The proliferation of cells was evaluated by BrdU assay. The results were analyzed with Dunns multiple comparison, Friedman, and Kruskal-Wallis tests. Results: No difference was seen in morphology of cells for either test material. Cells treated with MTA and Ca(OH)2 were reduced in number after 24 and 48 hours, respectively. A statistically significant difference was found in number of viable cells between test groups at 48 hours of incubation. The results of BrdU assay revealed low percentages of capable cells incorporating BrdU. Conclusions: The cytotoxic effects of the test materials- MTA and Ca(OH)2-on 3T3 cell lines were evaluated as cytostatic for 24 and 48 hours, respectively. But this effect was reversible because the incubated cells showed normal cell proliferation at 48 hours and 7 days, respectively; MTA showed a significantly shorter cytotoxic effect on the cells.