The upper airway dimension can be affected by many factors including orthodontic treatment. Previous studies showed large anterior teeth retraction decreased the length and volume of the upper airway. However, no studies have presented the effects of the amount of anterior teeth retraction on the upper airway. This study aimed to evaluate the effects of the amount of anterior retraction on the upper airway and hyoid position. The extraction group included 107 adult patients diagnosed with skeletal Class I relationship and dental Class I malocclusion who received four premolar extractions. Thirty adult patients who received non-extraction treatment were selected for the non-extraction group. The extraction group was divided into three subgroups depending on the retraction distance of lower incisors: E1 for small amounts, E2 for medium amounts, and E3 for large amounts of lower incisors retraction. Lateral cephalograms before and after treatment were collected. Comparisons of the three extraction subgroups showed differences between groups at SPP-SPPW, TB-TPPW and V-LPW. At the level of the soft palate (SPP-SPPW), E1 was different from E2. At the level of the base of the tongue (TB-TBBW), E1 was different from E3. At the level of the epiglottis (V-LPW), E1 was different from E2 and E3 (P<0.05). In summary, the retraction of lower incisors of more than 3 mm might decrease velopharynx, glossopharynx and hypopharynx.