To evaluate the application of midpalatal cortex osteotomy assisted rapid maxillary expansion for correction of maxillary transverse deficiency in young adults.Fourteen young adult patients with maxillary transverse deficiency were treated with midpalatal cortex osteotomy assisted rapid maxillary expansion. Lateral cephalogram and cone beam CT (CBCT) were taken before and 3 months after treatment. The width of basal bone, arch of maxilla and the torque of anchorage teeth were compared before and after treatment.The width of dental arch of maxilla was increased from 40.54±5.26 mm before treatment to 46.83±5.83 mm after treatment (<0.05) and the width of basal bone was increased from 64.86±4.16 mm to 67.60±4.66 mm (<0.05) at the plane of the maxillary first molars. Accordingly, the width of dental arch of maxilla was increased from 31.92±2.55 mm to 38.65±3.14 mm (<0.05) and the width of basal bone was increased from 43.33±3.70 mm to 45.78±4.57 mm (<0.05) at the plane of first premolar. And the torque of maxillary anchorage teeth were increased (<0.05).Midpalatal cortex osteotomy assisted rapid maxillary expansion is an effective micro-invasive method in expansion of basal bone and arch of maxilla for young adult patients with maxillary transverse deficiency.