Objective: Resin based dental materials are not stable in the oral environment and may release their components into biological media. These components may include substances such as triethylene glycol dimethacrylate (TEGDMA), which is a major co-monomer of dental resin materials. This release can trigger host immune and inflammatory responses against foreign materials, mediated by monocytes. The aim of this study was to investigate the possible cytotoxic effects of TEGDMA on human THP-1 monocytes.Material and Methods: THP-1 cells were exposed to various concentrations of TEGDMA (0.5 mM, 1 mM, 2 mM, 4 mM, or 8 mM) for 48 hours. An untreated group was used as control. The effects of TEGDMA on cell proliferation, cell viability and apoptosis were analyzed by light microscopy.Results: Cell proliferation was inhibited by 4 mM and 8 Mm TEGDMA. Increasing TEGDMA concentrations caused a decrease in cell viability. All TEGDMA concentrations used in this study had an apoptotic effect on THP-1 cells when compared with the control group.Conclusions: The dental monomer TEGDMA had an adverse effect on cell proliferation and exerted an apoptotic and toxic effect on THP-1 cells in a concentration-dependent manner.