Purpose: Seroma is the most frequently seen complication after the mastectomy and axillary dissection. The aim of this study was to analyze the effects of locally applied bovine collagen sponge and adipose-derived mesenchymal stem cells on seroma development in rats that undergone mastectomy and axillary dissection. Materials and Methods: Wistar albino rats, were randomly divided into 3 groups (n = 10 per group). For the rats in Group 1, 1 ml 0.09% NaCl was implemented. 2 x 106/kg adipose-derived mesenchymal stem cell was implemented within 1 ml 0.09% NaCl for the rats in Group 2, and 3 cm2 bovine collagen sponge were locally applied for the rats in Group 3. Adhesion scores, histopathological examination, E-cadherin expression and tissue seroma volume were evaluated. Results: The seroma volume of Group 3 were significantly lower than those of Groups 2 and 1 (p < 0.001). General adhesion scores of Group 3 were significantly higher than those of Groups 1 and 2 (p < 0.05). Statistically significant increase was observed in Group 3 compared to Group 1 in terms of fibroblast, neovascularization and collagen density (p < 0.05). Conclusion: Local application of bovine collagen sponge and ADSCs in rats, which have undergone experimental mastectomy and axillary dissection, can be told to decrease the seroma formation and to increase the neovascularization and collagen deposition. This effect is more significant in bovine collagen sponge group.