Purpose Accumulating evidence showed that probiotics therapy might be effective in treating diarrhea-predominant irritable bowel syndrome (IBS-D). This study aimed to evaluate the effectiveness and safety of probiotics therapy for the treatment of IBS-D. Methods We performed a comprehensive literature search in eight electronic databases, and gray literature from inception to August 4, 2021. Randomized controlled trials (RCTs) of probiotics therapy for the treatment of IBS-D were included and the quality was assessed using the risk of bias tool recommended by the Cochrane Handbook version 5.1.0. RevMan 5.4 software was used to perform the meta-analysis on the outcomes of IBS-D symptoms, abdominal pain, quality of life, and abdominal distension. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to assess the certainty of evidence. Results Ten RCTs evaluating 943 patients were identified. Only one study had unclear risk of bias, while nine studies had a high risk of bias. The meta-analysis results showed that, compared to the placebo, probiotics therapy significantly decreased the score of IBS-D symptoms (SMD = - 0.55, 95% CI: [- 0.83, - 0.27], P < 0.05), abdominal pain (SMD = - 0.43, 95% CI: [- 0.57, - 0.29], P < 0.05), and abdominal distension (SMD = - 0.45, 95%CI: [- 0.81, - 0.09], P < 0.05). There was no statistical difference in the quality of life. However, all the certainty of evidence was very low. Conclusion Very low certainty evidence showed that probiotics might be an effective treatment for improving the IBS-D symptoms, abdominal pain, and abdominal distension, in adult IBS-D patients. However, these conclusions should be supported by high-quality evidence.