Background/Aim: Vasopressin injected during myomectomy is known to effectively reduce bleeding but is sometimes associated with intraoperative vasoconstriction and hypertension due to systemic absorption. Although there is a growing preference for the use of diluted vasopressin, evidence of its effect and safety is still lacking. Patients and Methods: We performed a randomized controlled pilot trial to evaluate the effect and safety of vasopressin diluted in a constant volume during robot-assisted laparoscopic myomectomy (RALM), where a total of 39 women with uterine fibroids were randomly assigned into the following three groups (group 1, 0.2 IU/ml; group 2, 0.1 IU/ml; group 3, 0.05 IU/ml with a total of 100 ml of normal saline). The primary endpoint was to compare estimated blood loss (EBL), and the secondary endpoints were to compare postoperative value and drop ratio of hemoglobin, operation time, transfusion, hospitalization, and complications among the three groups. Results: There were no differences in the number and largest size of uterine fibroids, total weight of uterine fibroids, console time, and volumes of intravenous fluid administered during RALM among the three groups, whereas combined operation was performed more commonly in group 2 than in groups 1 and 3 (53.9% vs. 0 to 7.7%; p=0.01). The primary and secondary endpoints were also not different among the three groups. However, two patients in group 1 (15.4%) showed vasopressin-related hypertension. Conclusion: Vasopressin diluted in a volume of 100 ml showed an effective hemostatic effect and safety during RALM (Trial No. NCT04874246 in ClinicalTrial.gov).Uterine fibroids are the most common benign gynecologic condition in women, diagnosed in more than 25% of women of childbearing age. Despite its benign nature, uterine fibroids are associated with clinical symptoms, such as abnormal uterine bleeding, pain, and pressure in 25-50% of women, so there is still an ongoing clinical interest in effective treatment (1). Pharmacotherapy with non-steroidal anti-inflammatory drugs, hormonal agents, and gonadotropin-releasing hormone (GnRH) agonists is the first line of treatment for symptomatic uterine fibroids and invasive procedures, such as uterine artery embolization, or high-intensity focused ultrasound may be considered if there is a lack of response to the medical 431