BACKGROUND: Laparoscopic colorectal surgery has been proved to have similar oncological outcomes with open surgery. Due to the lack of tactile perception, surgeons may have misjudgments in laparoscopic colorectal surgery. Therefore, the accurate localization of a tumor before surgery is important, especially in the early stages of cancer. Autologous blood was thought a feasible and safe tattooing agent for preoperative endoscopic localization but its benefits remain controversial. We therefore proposed this randomized trial to the accuracy and safety of autogenous blood localization in small, serosa-negative lesion which will be resected by laparoscopic colectomy. METHODS: The current study is a single-center, open-label, non-inferiority, randomized controlled trial. Eligible participants would be aged 18-80 years and diagnosed with large lateral spreading tumors that could not be treated endoscopically, malignant polyps treated endoscopically that required additional colorectal resection, and serosa-negative malignant colorectal tumors (≤ cT3). A total of 220 patients would be randomly assigned (1:1) to autologous blood group or intraoperative colonoscopy group. The primary outcome is the localization accuracy. The secondary endpoint is adverse events related to endoscopic tattooing. DISCUSSION: This trial will investigate whether autologous blood marker achieves similar localization accuracy and safety in laparoscopic colorectal surgery compared to intraoperative colonoscopy. If our research hypothesis is statistically proved, the rational introduction of autologous blood tattooing in preoperative colonoscopy can help improve identification of the location of tumors for laparoscopic colorectal cancer surgery, performing an optimal resection, and minimizing unnecessary resections of normal tissues, thereby improving the patient's quality of life. Our research data will also provide high quality clinical evidence and data support for the conduction of multicenter phase III clinical trials. TRIAL REGISTRATION: This study is registered with ClinicalTrials.gov, NCT05597384. Registered 28 October 2022.