Background: and purpose: Preoperative anxiety is an important factor for postoperative complications, and many patients are using aromatherapy to relieve preoperative anxiety. This study aimed to evaluate the effect of aromatherapy on preoperative anxiety in adult patients. Methods: An electronic search of six databases (Cochrane Library, PubMed, Embase, CINAHL, CNKI, and WanFang Data) was conducted for full-text publications of trials published from the inception of the databases to February 20, 2020. All randomized controlled trials (RCTs) where aromatherapy was used for treatment of preoperative anxiety were included. Interventions included all types of aromatherapy compared to standard care or placebo. The primary outcome was self-rated anxiety and the secondary outcome was adverse effect. Two researchers independently screened and extracted relevant data. A random-effects model was utilized to calculate the effect size as mean difference (MD). Results: Our search retrieved 347 records. Thirteen trials were included for qualitative analysis, of which ten RCTs with 750 patients were included for meta-analysis. Most studies had a high or unclear selection and performance bias. Overall, aromatherapy was found to decrease preoperative anxiety significantly compared to the control group (MD = -3.95, 95%CI [-6.36, -1.53], P = 0.001). According to subgroup analysis, most subgroups showed a significant effect of aromatherapy on preoperative anxiety, except for the no treatment subgroup (MD: 5.40, 95%CI: 7.76 to 0.71) and female subgroup (MD: 3.96, 95%CI: 9.19 to 1.27). Conclusion: Aromatherapy may be an effective complementary treatment for preoperative anxiety. Nevertheless, due to methodological limitations of the included trials, further studies with strict control of the research design are required for firm recommendations.