Abstract: Objective Sleep is essential for maintaining physical and mental health,and sleep disorders are often present in hospitalized patients in the ICU,and aromatherapy is one of the non-pharmacological treatments for sleep disorders.This study aimed to investigate the effect of lavender essential oil on the sleep quality and anxiety level of patients in Hepatobiliary Surgery ICU. Methods A randomized controlled study was conducted with 60 patients in Hepatobiliary Surgery ICU.After informing the patients in both groups about the study,they were administered with two questionnaires,Pittsburgh Sleep Quality Index(PSQI) and the Self-Rating Anxiety Scale(SAS).The patients in the intervention group were given 2% lavender essential oil via inhalation for 15 days after which they were administered the same scales again to evaluate the sleep quality and anxiety.As for the control group,they were administered the same scales again after 15 days without the inhalation of lavender essential oil. Results The general situation of the intervention group and control group were compared and no statistical differences were found between the two groups;By comparison of sleep quality scores and anxiety scores before and after the treatment in the intervention group and the control group,the sleep quality value(8.68±2.96 vs. 6.80±2.83,t=2.514,P=0.015) and the anxiety score(56.43±9.48 vs. 47.93±7.70,t=3.812,P<0.001) of intervention group of patients were improved significantly after the treatment,while in the control group,the sleep quality scores and anxiety scores had no obvious improvement;furthermore,by comparison of the intervention group and the control group after the treatment,the intervention group's sleep quality score(6.80±2.83 vs. 8.48±2.60,t=2.394,P=0.020) and anxiety score(47.93±7.70 vs. 54.65±6.54,t=3.643,P<0.001) were improved significantly. Conclusion Lavender essential oil can improve quality of sleep and reduce the level of anxiety in patients in Hepatobiliary Surgery ICU.As a non-invasive,cheap,easily applicable,cost-effective,independent nursing intervention and appropriate for patients in Hepatobiliary Surgery,lavender essential oil could be applied in ICUs.