Introduction & Aim: Today, breast cancer is the biggest health threat to women. The current common treatments include surgery, chemotherapy, and radiotherapy. In most cancers, metastasis is the primary cause of treatment failure. Surgery and radiotherapy are effective on local tumors, but they cannot affect metastatic cancers. Chemotherapy is often used to treat metastatic cancers, the effectiveness of which is basically limited due to its toxic side effects at high doses. Due to the side effects of chemotherapy drugs, peptide therapy has become increasingly popular in the world. Accordingly, this study aims to investigate the effect of a designed bFGF antagonist peptide on inhibition of tumor growth in 4T1 metastatic breast cancer model and the serum levels of interleukin-8 and tumor necrosis factor-alpha.Methods: Female Balb/c mice (5-7 weeks old) were used in this study. Tumors were established using 4T1 tumor transplantation method. Treatment began after two weeks, when tumors reached an appropriate size. After that, the designed peptides at three selected doses were injected intraperitoneally for 14 days. Positive and negative controls were also used for each injection. The mice in the positive and negative control groups were injected with PBS and doxorubicin, respectively. Tumors size was measured every other day using a digital caliper, and their volume was measured using the formula: length × width2 × 0.5. After blood samples were taken from the mice’s eyes and plasma isolation was performed, interleukin-8 (IL-8) and tumor necrosis factor-alpha were measured by ELISA.Results: The data were analyzed by one-way analysis of variance (ANOVA) using SPSS. Given the value of p≤0.05, it can be concluded that peptide injection is effective in the reduction or inhibition of tumor growth. Significant differences are observed among the negative control group positive control, group, and the peptide-treated group. Conclusion: The results of this study showed that the anti-angiogenic peptide effectively inhibited the growth of the breast cancer and the results indicate that compared with the negative control group, serum levels of interleukin-8 and tumor necrosis factor-alpha are significantly different.