Arterial cannulation with ultrasound (US) guidance increases the success rate and reduces complications. US-guided vascular access has two main approaches: long axis in-plane (LA-IP) and short axis out-of-plane (SA-OOP) approaches. The purpose of this study was to compare performance time and possible complications between two techniques. After obtaining ethics committee approval and informed patient consent, a prospective and randomized trial was conducted at ASA I-III, patients between the ages of 20-70 years. 108 patients were scheduled for radial arterial cannulaton in patients undergoing elective surgery under general anesthesia. Patients were divided into two groups as LA-IP and SA-OOP approaches with sealed envelope randomized method. After induction of anesthesia, the distance between skin-to-artery and the diameter of radial artery in US-imaging was recorded. The successful cannulation time, the number of attempts, potential complications such as thrombosis, edema, vasospasm, hematoma and posterior wall puncture were recorded. Demographic and hemodynamic parameters were similar in two groups. The diameter and the depth of artery were also similar in both of groups. Cannulation time was shorter in LA-IP Group compared to SA-OOP (24 +/- A 17 s vs. 47 +/- A 34 s respectively, p < 0.05). The arterial cannulation by LA-IP approach increased the rate of cannula-insertion success at the first attempt (76 %) compared to SA-OOP approach (51 %). Posterior wall damage during arterial cannulation were found in 30 patients with SA-OOP Group (56 %) and 11 patients with LA-IP Group (20 %), (p < 0.05). In our study, the use of LA-IP approach during US-guided radial artery cannulation has higher success rate at first insertion. We also found LA-IP approach results in shorter cannulation time and decreased the incidence of complications.