Objective:To clarify the treatment effects of T4K on Class II division 1 malocclusion.Methods:Twenty patients (10 girls and 10 boys) aged 8~10 years old with Class II division 1 malocclusion were treated with T4K appliance(Myofunctional Research Co., Queensland, Australia).A control group of 20 patients aged 9~11 years old with untreated Class II division 1 malocclusions was used to eliminate the possible growth effects. Lateral cephalograms were taken before and after treatment. Final cephalograms were taken (12.1?1.8) months after T4K application.The subjects in control group were observed for (11.2?2.1) months.The mean and standard deviations for cephalometric measurements were analyzed by paired-samples and independent-sample t-tests. Results:In the treated subjects significant changes including anterior rotation and sagittal growth of the mandible, increased SNB and facial height, reduced ANB, increased lower incisor proclination, upper incisor overjet reduction were observed.Conclusion:T4K appliance is effective in the treatment of class II division 1 malocclusion.