Aim: Quxie capsule(QX), a TCM compound, had shown benefit on survival outcomes for metastatic colorectal cancer(mCRC) patients and could inhibit tumor growth through immune regulation. This study aimed to evaluate whether such effect is associated with gut microbiome modulation. Method: We conducted a randomized double-blinded placebo controlled clinical trial in Xiyuan Hospital, China Academy of Chinese Medical Sciences. All patients were randomly assigned into QX or placebo control group. Before and after 1-month interventions, we collected patients' stool samples for microbiome analysis by 16s rRNA sequencing approaches, as well as blood samples to analyze T lymphocyte subsets by flow cytometry methods. Microbiome analysis among groups was done through bioinformation analysis platform. The study had been proved by the ethics committee of Xiyuan Hospital (2016XLA122-1) had been registered on Chinese Clinical Trial Registry (registration number: ChiCTR2000029599). All patients consented before enrollment. Results: We randomly assigned 40 patients and 34 were finally analyzed. Among them, 29% were female, with an average age of 63 years old, and 74% had liver or lung metastasis. Both CD4 T(TH) cell and CD8 T(TC) cell counts increased after QX treatment, while TH cells were significantly more in QX than in control group (737 vs 449, P = .024). Microbiome community analysis on Class level showed that the proportion of Actinobacteria declined in the control group, but significantly increased after QX treatments (0.83% vs 4.7%, P = .017). LEfSe analysis showed that after treatments, samples from QX group were highly related with Oscillibacter, Eubacterium, and Lachnospiraceae. RDA analysis showed that after QX interventions, stool samples and microbiome species had relevance with TC/TH cells counts but were not statistically significant. Heatmap analysis on Genus level revealed that after QX treatments, higher amounts of TH cells were significantly associated with less abundance of g_Bifidobacterium (coef. -0.76, P = .002), Collinsella (coef.-0.61, P = .02), Ruminiclostridium_9 (coef. -0.64, P = .01). Conclusion: QX capsule could enhance TH cells level among mCRC patients and increase the abundance of gut anticancer bacteria such as Actinobacteria as well as butyrate-producing bacteria such as Lachnospiraceae. These results indicated that QX capsule might have the property of dual effects of antitumor and immunity enhancement, both mediated by the microbiome.