Objective To investigate the effect of midpalatal corticotomy (MCO) assisted maxillary skeletal expander (MSE) on maxillary transverse skeletal measurements in adult patients with maxillary transverse deffciency (MTD). Methods A total of 48 adult patients with MTD treated in Chengdu Stomatological Hospital from January 2022 to June 2024 were selected, and they were divided into the control group and the observation group according to treatment methods, with 24 patients in each group. The control group received MSE alone, and the observation group received MCO combined with MSE. The maxillary transverse skeletal measurements, dental arch and tooth inclination indicators and expansion duration were compared between the two groups. Results At T1 and T2, the M1-BW1, P1-BW1 and MSO in the observation group were higher than those in the control group (P<0.05). At T1 and T2, the proportions of skeletal expansion component in the observation group were higher than those in the control group (P<0.05). At T1, the NW of the observation group was higher than that of the control group (P<0.05). There was no statistically signiffcant difference in MAW between the two groups at different time points (P>0.05). There was no signiffcant difference in U6-PP between the two groups at T1 (P>0.05). At T2, the U6-PP in the observation group was lower than that in the control group (P<0.05). The expansion duration of the observation group was shorter than that of the control group (P<0.05). Conclusion MCOassisted MSE can effectively improve maxillary transverse skeletal measurements in adult patients with MTD. It can increase basal maxillary width, facilitate midpalatal suture opening, shorten expansion treatment course, reduce buccal compensatory inclination of anchor teeth, and achieve higher proportion of skeletal expansion compared with MSE alone.