Background: Colorectal Adenomatous Polyp (CAP) was one precursor of colorectal cancer (CRC) and having a high chance of developing into CRC. There was a lack of conclusive chemoprevention evidences to prevention new CAP occurrence in post-polypectomy. Xiaoai Jiedu Decoction, Chinese National Medical Professor (Zhou Zhongying)'s experience formula, has been used to treat new CAP occurrence in post-polypectomy from the 20th century in China. However, clinical research of Xiaoai Jiedu Decoction in the treatment of CAP recurrence was lack. We design this study to evaluate the efficacy and safety of Xiaoai Jiedu Decoction in the treatment of new CAP occurrence in post-polypectomy on colonoscopy. Methods/Design: A randomized, controlled, blind and multicenter trial to evaluate the efficacy and safety of Xiaoai Jiedu Decoction is proposed. CAP patients (after complete polypectomy under colonoscopy) will be randomly assigned into Xiaoai Jiedu Decoction group and Xiaoai Jiedu Decoction mimetic agent group. Patients will receive 6-course treatments and a 2-year follow-up. Follow-up colonoscopy will be anticipated to perform in 1 and 2 years after the baseline examinations. The primary outcome measure is the new CAP occurrence in 1 and 2 years. The secondary outcome measure is the occurrence of advanced adenoma in 1 and 2 years. Discussion: This study will provide objective evidences to evaluate the efficacy and safety of Xiaoai Jiedu Decoction as an adjuvant treatment for new CAP occurrence in post-polypectomy.