Summary Background Tong‐Xie‐Yao‐Fang (TXYF) is a Chinese herbal formula for treating chronic diarrhoea accompanied by abdominal pain. The results were inconsistent in previous trials examining its effect. Aim To study the efficacy of TXYF granules for treating diarrhoea‐predominant irritable bowel syndrome (IBS‐D). Methods We performed a double‐blind, placebo‐controlled randomised trial and enrolled 160 participants with IBS‐D. The participants had VAS scores ≥3 cm in IBS‐D global symptoms and ≥2 days in a week with abdominal pain and loose stools (Bristol score 5, 6 or 7). They were randomly assigned to received TXYF or placebo during a treatment period of 4 weeks, and they were followed up for 8 weeks after treatment. The primary outcome was adequate relief of IBS‐D global symptoms for at least 2 of 4 weeks during weeks 1‐4. Secondary outcomes included mean weekly VAS scores of IBS‐D major symptoms, mean weekly stool frequency, mean weekly Bristol score, and adverse events. Results 155 of 160 patients completed the trial. We found a significantly higher rate of adequate relief of global symptoms in TXFY group during weeks 1 to 4 (57.5% vs 37.5%, χ2 = 5.6391, P = 0.017); logistic regression analysis showed a similar result (OR 2.2, 95% CI 1.2‐4.4, P = 0.016). Most of the secondary outcomes showed superiority of TXYF over placebo in weekly assessment from week 3 to week 7. The adverse event rate was low in both groups (3.8% vs 3.8%, P = 1.000). Conclusion During a 4 week trial, TXFY granules were superior to placebo in controlling symptoms of IBS‐D. Linked ContentThis article is linked to Vitta and Sayuk and Chen et al papers. To view these articles visit https://doi.org/10.1111/apt.14902 and https://doi.org/10.1111/apt.14906.