The Star Excursion Balance Test (SEBT) is a dynamic balance test used for the screening of injuries in the fields of sports; however, we do not clearly understand what factors of the SEBT are associated with the occurrence of injury. We hypothesized that the trunk movement would be a key factor related with the maximum reach distance (MRD) of the SEBT. The purpose of this study was to examine the relationship of the MRD during the SEBT with trunk lean angles and ankle flexibility. We recruited 19 healthy male athletes (age: 21±0.8 years, height: 170.2 ± 6.6 cm, weight: 65.2 ± 6.9 kg) and measured the MRD of the SEBT including anterior, posteromedial and posterolateral directions, the trunk lean angles at MRD, and the maximum ankle dorsi-flexion angle (DFA). The trunk lean angles were measured with the Direct Linear Transformation (DLT) method. The DFA was measured by the weight-bearing-lunge-test. We used Pearson’s correlation coefficient. There were positive correlations between the anterior-MRD and DFA; the posteromedial-MRD and the lateral trunk angle; the posterolateral-MRD and the forward trunk angle (r =.58, r =.47, r =.62, p<0.05, respectively). For future study, we need to consider the trunk movement and to focus on other factors such as muscle strength, muscle activities, center of mass, and center of pressure, which contribute to the MRD of the SEBT.