BackgroundImproving the understanding of shoulder function for badminton players would develop injury preventive programs. However, no studies on shoulder function reference parameters of badminton players when controlling for age and sex have been found. ObjectivesTo examine the differences in shoulder function between elementary school-age badminton players and university badminton players using shoulder range of motion. DesignCross-sectional study. SettingTesting at elementary school and university. Participants67 players (7-12 year-old players and 18-22 year-old players) without shoulder injury experience. Main outcome measuresShoulder range of motion (ROM) included internal rotation (IR), external rotation (ER), and total ROM (TROM). ResultsSignificant differences in shoulder IR of both sides (dominant: 97.67° vs 77.78°, p < 0.001; nondominant:104.70° vs 88.89°, p < 0.001), dominant ER (126.30° vs 115.98°, p = 0.013), TROM of both sides (dominant: 222.97° vs 193.76°, p < 0.001; nondominant: 222.90° vs 200.10°, p = 0.001), and TROM loss (-0.06° vs 6.34°, p = 0.047) existed between elementary school-age and university players. Significant differences in IR of both sides existed between male elementary school-age and university players (dominant: 98.38° vs 72.50°, p < 0.001; nondominant: 106.72° vs 83.99°, p < 0.001) as well as in female players (dominant: 95.25° vs 82.84°, p = 0.007; nondominant: 103.01° vs 93.57°, p = 0.035). Additionally, significant differences in IR of both sides (dominant: 72.50° vs 82.84°, p = 0.016; nondominant: 83.99° vs 93.57°, p = 0.012) and TROM of both sides (dominant: 188.24° vs 199.05°, p = 0.025; nondominant: 192.43° vs 207.44°, p = 0.002) existed between male and female university players. ConclusionsCompared with university badminton players, elementary school-age badminton players showed significantly greater shoulder IR and TROM of both sides and dominant ER while significantly smaller TROM loss. However, regardless of sex, no significant differences of bilateral deficit for glenohumeral rotation existed between elementary school-age and university badminton players.