Objective To evaluate the diagnostic value of high-frequency ultrasound in the diagnosis of supinator syndrome (SD). Methods Ten patients with supinator syndrome (SD group) and 20 healthy volunteers (control group) underwent ultrasonographic examination. Axial and long-axis views of the radial nerve were taken where the nerves enters the supinator muscle entrance. The maximum transverse diameter and anteroposterior diameter were also measured. Results High-frequency ultrasound clearly revealed the images and course of radial nerve deep branch in two groups. The SD group had swollen nerves and the maximum transverse diameter and anteroposterior diameter were (3.50?0.39)mm and (4.30?0.47)mm,respectively,which were significantly larger than in the control group [(1.10?0.17)mm,t=-29.67,P=0.00;(1.00?0.16)mm,t=-36.72,P=0.00). The causes (including synovial cyst nearby and radial artery recurrent branch) of nerve entrapment were revealed directly in 4 patients in SD group. Conclusions High-frequency ultrasound can clearly display the radial nerve deep branch around the elbow joint. SD patients have swollen nerves at the entrance of the supinator muscle,where the diameters of these nerves are abnormally enlarged.