Objective To analyze the effects on the morphology of temporomandibular joint（TMJ） of the adult with the low angle Class Ⅱ malocclusions before and after orthodontic treatment comparatively. To provide the references for the orthodontic treatment of the adults. Methods 19 adult patients with low angle Class Ⅱ malocclusions were chosen and treated with Damon self-ligating braces. The examinations of 16-slice spiral CT were taken before and after the orthodontic treatment. The parameters of skeletal morphology of TMJ were measured in the multiplanar reconstruction（MPR） images. The results were analysed statistically. Results The rate of condyles in a center position in the glenoid fossa after the treatment was 52.6%（20/38）, and the rate of retrodisplacement was 31.6%（12/38）. The position of the condyles before and after the orthodontic treatment had significant differences（P
