Background: Triazene compounds have many applications in various fields such as anticancer drugs. In this study, we aimed to find out anti-cancerous effects of 1-(3, 5-dichlorophenyl)-3-(2-ethoxyphenyl) triazene on 4T1 cell line and induced breast cancer in mice. Materials and methods: 4T1 cell line was cultured and then treated for 24h with different concentrations of new triazene compound. Cell viability was assessed by MTT assay. For tumor induction, we used 7-8 weeks old Balb/C mice. Then 4T1 cells were injected subcutaneously with appropriate concentration. When tumor observed, mice were randomly assigned to groups. Mice were treated with different concentration of new triazene compound. Tumor sizes in each group were compared before and after the treatment. Expression of Bax gene was analyzed by RT-PCR. Results: MTT assay results shows that IC50 for new triazene compound on 4T1 cell line in 24h was 30µ Mol. Also analysis of tumor size shows a significant reduction at triazene treated groups compared with the control group. RT-PCR result shows increase in Bax gene expression at triazene treated groups compared with the control group. Conclusion: New triazene compound could reduce 4T1 cell viability invitro and also could reduce tumor size invivo. Also, it could induce apoptosis in tumor tissues by increase in Bax gene expression.