Eight dogs with histologically confirmed mammary adenocarcinoma were enrolled in a study to determine if an herbal formula, Mammosol (a proprietary blend of 28 herbal ingredients), could prolong survival times compared to two previous reports in dogs having surgical excision alone or surgical excision in combination with chemotherapy. Dogs were excluded from the study if they had had chemotherapy or radiation therapy before, during or after the herbal supplement, in order to determine if the supplement alone would extend survival times. All dogs had surgical excision of their cancer and no evidence of metastasis on thoracic radiographs. All dog were administered 0.022 gm/kg of Mammosol twice daily for 2 years and monitored with thoracic radiographs and physical examinations at 3, 6, 9, 12, 18 and 24 months post surgery. Serum biochemical tests for liver and kidney function were evaluated during the study period to monitor for unexpected toxicity. In this study, 7 of the 8 dogs lived greater than 2 years. The dog that lived less than 2 years only received half the dose of herbs due to improper caretaker compliance. Survival rates were significantly increased in the dogs that had surgical excision and Mammosol as compared to previously published results of dogs that had surgery alone (p value 0.001) and dogs with surgery and chemotherapy (p value 0.05) using the discrete Bonferroni method. Further investigations of Chinese herbal treatments for mammary cancer therapy are warranted.