Certain food preservatives, including potassium benzoate, have been shown to possess carcinogenic properties. This study investigated the cytotoxic effects of potassium benzoate, a common food additive, on HepG2 liver cancer cells and THLE2 non-tumorigenic liver cells. Using the Neutral Red assay, we observed a concentration-dependent decrease in cell viability for both cell lines, with HepG2 cells showing higher sensitivity. The IC50 values were determined to be 72.50 µg/mL for HepG2 cells and 645.7 µg/mL for THLE2 cells, indicating potassium benzoate's potential cytotoxicity on both malignant and non-malignant cells. Flow cytometry analysis revealed that potassium benzoate treatment induced G2/M phase arrest in HepG2 cells, with a significant increase in the proportion of cells in the G2/M phase from 12% to 43%. Gene expression analysis using qRT-PCR demonstrated upregulation of p53, Bax, and p21, while Bcl-2, cyclin B1, and CDK1 were downregulated. These findings suggest that potassium benzoate has a high potential for cytotoxicity and genotoxicity when used as a food preservative. This study contributes to the growing body of evidence on the potential health impacts of food additives and underscores the need for further research into their long-term effects on human health.