Purpose The aim of this study was to compare the cervical, thoracic, and shoulder posture according to the onehanded and twohanded use of smartphone while sitting position in university students. Methods Thirty subjects participated in this study. Subjects were asked to perform while sitting position between the onehanded and twohanded use of the smartphone. To quantitatively assess the cervical and thoracic flexion of subjects, the angle was measured using the smartphone application (Goniometer Pro). The shoulder level of subjects was measured using a scoliometer. Results The cervical, thoracic flexion angle and shoulder level were significantly greater when sitting while sitting of one and twohanded use of the smartphone compared to that of normal sitting without using a smartphone (p<0.05). The shoulder level was significantly greater when onehanded use of the smartphone compared to that of normal sitting without using a smartphone (p<0.05). The shoulder level was significantly greater when onehanded use of the smartphone compared to that of twohanded use of the smartphone (p<0.05). Conclusion Study results indicate that habitually using a smartphone while onehanded use of a smartphone in sitting position could be a potential risk for nonneutral trunk posture.