Background: Cancer is one of the most complicated diseases with various treatments, which each has its special side effects. So, pharmaceutical companies are intended to develop new drugs with minimum side effects. Objectives: The current study aimed to investigate the cytotoxicity effects and the redox potential of alcoholic extract of Oleaster leaf on liver carcinoma cell line (HepG2). Methods: Oleaster leaves were collected from Qazvin (Iran), and the alcoholic extract of the plant leaves was prepared. HepG2 cells were cultured in DMEM medium and treated with 50, 100, 200, 400, and 600 μg/mL of the extract. The cytotoxicity effect of the extract was evaluated using the MTT and the Neutral Red assays. Redox potential in HepG2 cells was assessed using NO, catalase, and GSH tests. The expression of Bax and bcl-2 genes in HepG2 cells was evaluated for apoptosis analysis. Results: The results showed that the extract could significantly (P < 0.001) reduce the viability of HepG2 cells. Also, the extract significantly increased the amount of released NO, catalase activity, and GSH concentration. RT-PCR results showed that Oleaster leaf extract significantly change the expression of bax and bcl-2. Conclusions: The results showed that the leaves of the Oleaster plant contain compounds with cytotoxicity properties, so it can be considered as a potent candidate for liver cancer treatment.