Background and Aim: Resin cements are used widely in restorative dentistry regardless of their biocompatibility. The aim of this study was to compare the cytotoxicity of two categories of dental cements consisting of three chemically set cements (Fuji I, Fuji PLUS and Harvard) and two dual curing cements (BisCem and Duo-Link) by use of MTT assay. Methods and Materials: In this experimental study, four round-shaped samples of each specimen were placed in DMEM culture medium for 24, 48 and 72 hours. The extracts from each sample were applied on L929 mouse fibroblasts. At the end of each period, MTT assay was carried out to estimate the mitochondrial respiration. Data were analyzed by one-way analysis of variance (ANOVA) followed by Tukey's post-hoc test. The degree of cytotoxicity for each sample was determined according to the reference value of the control group. Results: Fuji I cement showed the least cytotoxicity while Harvard and BisCem cements showed the highest cytotoxic effect. The differences were not significant compared to the positive control (distilled water). Conclusion: This study showed that dental cements are capable of eliciting biological response in gingival and pulpal cells. They present a potential risk of tissue damage which depends on the cement's brand and curing modes.