Objective To systematically evaluate the effect of dexmedetomidine on postoperative cellular immune function in patients with malignant tumor.Methods The Medline,Cochrane Library,EMBASE,PubMed,OVID,Superstar Foreign Languages Database and Chinese Database,CNKI,Chinese Biomedical Literature CD-ROM Database and Wanfang Database were searched,and the publication was not limited by language or time.The randomized controlled trials involving the effect of dexmedetomidine on postoperative cellular immune function in patients with malignant tumor were collected.The evaluation indexes included the levels of whole blood T lymphocyte subsets CD3+,CD4+,CD8+ and natural killer cells and ratio of CD4+/CD8+.Meta-analysis was conducted using the Cochrane Collaboration's RevMan 5.2 software.Results Twelve prospective randomized controlled trials involving 692 patients were included in our meta-analysis.Compared with control group,the levels of CD3+,CD4+ and natural killer cells and ratio of CD4+/CD8+ were significantly increased at 1 day after operation (P＜0.01),and no significant change was found in the level of CD8+ in dexmedetomidine group (P＞0.05).Conclusion Dexmedetomidine can improve postoperative cellular immune function in patients with malignant tumors.