The purpose of the study was to evaluate the cytotoxic effects of polycarboxylate cements and zinc phosphate cements in vitro. Human fibroblasts were cultured in ${alpha}$-MEM, and each cement was manually mixed and filled in glass ring cylinder (8${ imes}$8mm in diameter, in height.) Cement filled cylinders were placed in the center of the dish (35mm in diameter) containing 3ml of ${alpha}$-MEM. Millipore filters to simulate dentinal barrier were also placed between the cylinder and the dish, then stored in 5% $CO_2$ containing chamber for 1 and 2 weeks at the temperature of $36.6^{circ}C$. The results of the experiments were analyzed by counting the cells in the period of one week and two weeks respectively, and were assessed by calculating the cell multiplication rate and the relative growth rate. The experimental groups and the control group were compared. The results of the study were summarized as follows. 1. Durelone brand of the polycarboxylate cements showed marked cytotoxicity after one week, but after two weeks the toxicity decreased remarkably. Poly-F brand exhibited moderate cytotoxicity after one week, but after two weeks the toxicity slightly decreased. HY-BOND brand was weakly cytotoxic after one week, but after two weeks the toxicity became significant. 2. The cytotoxicity of the zinc phosphate cements was negligible after one week, but after two weeks Lee Smith brand revealed considerable cytotoxicity. 3. In general, the zinc phosphate cements were less cytotoxic than the polycarboxylate cements.