Abstract: Objective To evaluate the palatal contour changes in young adults with posterior crossbite after rapid maxillary expansion. Methods The observation group included 15 young adult rapid maxillary expansion （YA-RME） subjects, while the control group included 22 YA-RME subjects in mixed dentine.. Measurements of palatal contour were all taken at the pre-treatment time（T1） and post-treatment（T2）, which were derived by the use of 3-dimension laser scanning technology（3-DLST）. SPSS 11.0 software was used to determine if there were significant differences between 2 time periods and between 2 groups. Results 1）There was no significant difference between YA-RME group and control group in the increase of palatal width at gingival height and at midpalate（P＞0.05）, but significant difference in palatal width difference（P＜0.05）. 2）There were significant differences both in molar angle decrease and palatal vault angle increase（P＜0.05）. Conclusion YA-RME is a clinically effective method to expend maxillary dental arch and correct posterior crossbite.