Background: Chemotherapy, as one of the main treatments for patients with colorectal cancer (CRC), brings clinical benefits with varying degrees of gastrointestinal reactions. Post-chemotherapy diarrhea is one of the factors affecting the quality of life of cancer patients. In severe cases, it can cause interruption of the chemotherapy process and even be life-threatening. Probiotics’ role in preventing post chemotherapy diarrhea in CRC patients has not been proven. Methods: This meta-analysis was registered with PROSPERO (CRD42023480526). A comprehensive search using subject terms and keywords was conducted to identify randomized controlled trials. Six databases, CNKI, Wanfang, VIP Journals, PubMed, EMBASE, and Web of Science, were searched from their inception until January 16, 2024. The search terms used included “cancer,” “tumor,” “chemotherapy,” “diarrhea,” “probiotics,” and “placebo.” Clinical studies using probiotics to intervene in post chemotherapy diarrhea in CRC patients were included and data were independently extracted for each study. Meta-analysis and sensitivity analysis were performed using RevMan 5.4 and Stata 14 software. Results: Eighteen studies involving 1526 patients were included in this analysis. Meta-analysis demonstrated that probiotics significantly reduced the incidence of diarrhea following chemotherapy in the probiotic group compared to the control group (risk ratio, 0.51; 95% confidence interval: [0.40–0.64]; P = .029). Meanwhile, the use of probiotics significantly shortened the duration of diarrhea (risk ratio: -2.38, 95% confidence interval: [-2.96 to 1.80]). Furthermore, probiotics have been shown to positively affect other gastrointestinal symptoms. Specifically, probiotics significantly alleviated bloating, nausea/vomiting, loss of appetite, and abdominal pain. However, no significant differences were observed in the effects of probiotics on enteritis, tumor necrosis factor-α, diamine oxidase, and interleukin-6. Conclusion: The comprehensive analysis of 18 randomized controlled trials provided compelling evidence that the probiotics have significant clinical value in preventing the onset of diarrhea, shortening the duration of diarrhea, and alleviating chemotherapy-induced gastrointestinal symptoms.