BACKGROUND: Although the first attempt success rate of radial artery cannulation has been significantly improved by using dynamic needle tip positioning (DNTP) method, there are still problems with long cannulation time. We hereby observe the effect of ultrasound angle for radial artery cannulation in adult patients. METHODS: Adult patients scheduled to undergo elective surgeries with continuous invasive blood pressure monitoring were included and randomly allocated into either a U-P-artery (ultrasound probe perpendicular to the artery) or U-P needle (ultrasound probe perpendicular to the needle) group. The primary outcome measure was cannulation time at the first attempt, the secondary outcome measures included the first attempt success rate, number of attempts and the total puncture procedure duration. In addition, the incidence of complications was included as secondary outcomes. RESULTS: Fifty-nine patients were evaluated finally. The cannulation time at the first attempt in U-P-needle group (N.=28) was significantly lower than that in U-P-artery group (N.=31; median [IQR]: 16 [13.5-20] seconds vs. 41 [25.554.5] seconds, P<0.001). The total puncture procedure duration in group U-P-needle was also shorter than that in the group U-P-artery (median [IQR]: 17.4 [13.5-20] seconds vs. 52.2 [25.5-54.5] seconds, P<0.001). No significant difference was observed with respect to first-attempt success rate (96.4% vs. 93.5%, relative risk: 0.97, 95% CI: 0.863-1.0907, P=0.615). The number of attempts showed no statistical difference as well. CONCLUSIONS: The usage of the U-P-needle approach could remarkably reduce radial arterial cannulation time at the first attempt as well as total puncture procedure duration, comparing with the U-P-artery approach. (Cite this article as: Zhang S, Liu T, Liu Y, Mei W. Effect of ultrasound angle for radial artery cannulation in adults: a randomized controlled trial. Minerva Anestesiol 2022;88:230-7. DOI: 10.23736/S0375-9393.22.16090-6)