Abstract: Abstract：Objective To evaluate the clinical effect of the orthodontic treatment after extracting two mandibular premolars in adult skeletal cross-bite subjects. Methods Eighteen borderline adult skeletal cross-bite cases from 18 years old to 30 years old were studied. In these cases, first or second mandibular premolars were extracted. Lateral cephalometric radiographs were taken before and after treatment for analysis of all indicators. Results At the end of the treatment, normal overjet and overbite were established in class Ⅲ molar relationship and classⅠcanine relationship. There appeared to be no significant hard tissue changes (P≥0.05). L1-MP angles decreased by 8.1°on average, U1-L1 angles increased by 7.7°on average, L1-NB angles decreased by 7.3°on average, L1-NB distances decreased by 4.8mm on average. Statistically significant differences were found in these changes (P<0.01). The soft-tissue profile improved significantly. Li-E distances, Li-H distances and Li-RL2 distances decreased by 3.2mm、3.4mm and 4.1mm on average respectively. Statistically significant differences were found in these changes (P<0.01). Conclusion Success in the treatment of adult skeletal cross-bite can be achieved clinically by extraction of 2 lower premolars. All the patients get good occlusion and straight profile tendency.