BACKGROUND: Patients with gastrointestinal cancer often have impaired immune function after surgery. This study aimed to assess the efficacy of Sijunzi decoction (SJZD) on immune function in patients with gastrointestinal cancers after surgery. METHODS: The electronic databases, including CNKI, Wanfang, SinoMed, Weipu, PubMed, Web of Science, EMBASE, and Cochrane databases were retrieved (March 1, 2024), and the randomized controlled trials (RCTs) that met the criteria were included. Methodologic quality assessment of RCTs was performed using the Cochrane risk of bias tool. The data of RCTs were acquired and analyzed by meta-analysis by Review Manager 5.3, and the quality of the evidence followed the Grading of Recommendations, Assessment, Development and Evaluations approach. This research was registered in the International Platform of Registered Systematic Review and Meta-analysis, 202440001. Based on the network pharmacology, relationships between key genes of SJZD and tumor-infiltrating immune cells in gastrointestinal cancers were explored. RESULTS: Thirteen articles (RCTs) were included, containing 1010 patients with gastrointestinal cancers after surgery. The results of meta-analysis revealed that SJZD with conventional therapies could improve CD3+ T lymphocyte (mean difference [MD] = 5.73, 95% confidence interval [CI]: 2.07-9.39, P = .002), CD4+ T lymphocyte (MD = 5.86, 95% CI: 3.90-7.82, P <
.00001), CD4+/CD8+ (MD = 0.29, 95% CI: 0.15-0.43, P <
.0001), and reduce CD8+ T lymphocyte (MD = -2.44, 95% CI: -4.03 to -0.85, P = .003) compared with conventional therapies alone. In addition, the funnel plot showed the included RCTs might have publication bias. The Grading of Recommendations, Assessment, Development and Evaluations classification showed low-quality evidence for CD4+, CD8+, and CD4+/CD8+, and very low-quality evidence for other indicators. The network pharmacology results suggested that SJZD may exert effects by regulating the immune cells in the microenvironment of gastrointestinal cancers. CONCLUSION: SJZD could enhance the immune function of patients with gastrointestinal cancers after surgery. Due to the low quality of articles, more high-quality RCTs are needed to improve the level of evidence.