The aim of this study was to evaluate the cytotoxic effects of an enzymatic mouthwash and of a chlorhexidine mouthwash on human gingival fibroblasts. The metabolic activity of the fibroblasts exposed to each mouthwash was assessed by the MTT assay and the protein content was assessed by the SRB assay. The flow cytometry was used to evaluate the cell cycle and the types of cell death. The oxidative status was evaluated through the DCF and the DHE probes and the intracellular GSH concentration and the mitochondrial membrane potential through JC-1. The cytotoxicity of both mouthwashes was found to be dependent on the exposure time and on the concentration. However, the cytotoxicity of the enzymatic mouthwash was found to be lower than that of the chlorhexidine mouthwash. A trend towards increased oxidative stress was observed for both mouthwashes. After exposing the fibroblasts to the mouthwashes, a G2/M phase block was observed and cell death occurred predominantly by necrosis. The effects of chlorhexidine on fibroblasts were identified at lower concentrations than those used in clinical practice. Therefore, the use of chlorhexidine as an antiseptic in surgical and postoperative situations should be limited. In order to clarify the clinical significance of the enzymatic mouthwash cytotoxicity new clinical studies will be necessary.