Objective：To investigate the condylar position differences in three dimensions between centric relation（CR） and maximum intercuspation（MI） in patients with unilateral posterior crossbite and to explore the possible correlation between transverse discrepen－cy and CR-MI displacement. Methods：Thirty-three unilateral posterior crossbite cases（experimental group） and thirty-three normal occlusion cases（control group） were evaluated. Mounting dental casts on articulator with CR bite record and Roth centric registration technique was employed. The three dimensional condylar displacements between CR and MI were measued by measure condyle displacement（MCD）. The arch width of the first molar were measured by digital caliper. Independent t-test，paired t-tests and pearson correlation were used to do statistical analysis；P<0.05 signifies statistical significance. Results：（1）The positive rate of CR-MI dis－crepency in the unilateral posterior crossbite group was higher than that in the normal occlusion group（χ2=38.018，P=0.000）. （2）In the experimental group，the distraction of the condyles was significantly greater on the crossbite side than on uncrossbite side in the vertical plane（t=2.719，P=0.010）. The condylar displacement observed in sagittal plane showed no significant difference between two sides（t=-0.134，P=0.894）. （3）Maxillary intermolar width was significantly smaller in the experimental group than in control group（t=-4.008，P=0.000）；the lower arch width showed no significant differences between groups（t=1.653，P=0.103）. There was no significant corre－lation between transverse arch discrepency and CR-MI displacement in three dimensional directions. （4）The positive rate of occlusion interferences in experimental group（90.91%） was significant higher than that in control group（66.67%， χ2=5.802，P=0.033）. The oc－clusion interferences were mostly found on the posterior teeth. Conclusion：Transverse arch discrepancy influence condyle position in patients with unilateral posterior crossbite. Among them，the vertical displacement is the most significant one. In order to get better treatment，it is important to measure the condylar dis－placement and unmask real jaw relationship before the compre－hensive orthodontic treatment starts.