Background: The occurrence of seroma formation and long-term wound healing remain challenging complications after modified radical mastectomy. Sapylin is a drug used to reduce seroma formation and enhance wound closure, but these results remain controversial. We aimed to investigate the potential mechanism. Methods: A prospective, consecutive cohort study included 120 patients diagnosed with breast cancer who underwent modified radical mastectomy was designed. Patients were randomized into two group, using or not using OK-432 (sixty patients per group) during surgeries. Patients' drainage fluids were collected for three days after surgery. Inflammatory cytokines and chemokines were measured with ELISA assays. The proliferative, migratory, and angiogenic capacity of HUVEC and HFL1 cells HUVEC and HFL1 cells were measured after being treated with drainage fluids. Results: Our clinic data showed that there was no statistical significance between the two groups in patient characteristics before surgery. However, the outcomes of patients in experimental group were significantly better than those in control group. In vitro studies, the results of ELISA assays showed that several cytokines, including IL-1a, IL-6, TGF-beta 1, bFGF and VEGF were increased in the drainage fluids treated with Sapylin. The proliferative, migratory, and angiogenic capacity of HUVEC and HFL1 cells were significantly enhanced after being treated with Sapylin group drainage fluids. Conclusion: Sapylin could stimulate the body to secrete a variety of cytokines to promote wound healing by promoting endothelial cell proliferation and migration, angiogenesis and by increasing fibroblast migration and collagen deposition.