Objective : Overjet is a horizontal relationship between maxillary and mandibular incisors. Normal range from overjet is 2-4 mm. Increased overjet is marked by maxillary incisor’s protrusion. A 6 mm overjet will have impact on psychological and social relationship of children due to the aesthetics of the face profile. Increased overjet has relationship with Class II Angle malocclusion, Class II skeletal sagittal relationship, and mandibular retrognathia. Clinical problem caused by increased overjet in children are maxillary permanent incisors trauma in growing age, damaged periodontal tissue, lip incompetency, social impact such as lack of confidence in children, and also increased overjet has a close relationship with Temporomandibular Disorder (TMD) sign and symptoms.Methods : Increased overjet case can be managed by maxillary retraction of labial segment and increasing mandibular labial segment. Case management are based on skeletal and soft tissue pattern and patient’s age. Reducing overjet can be based on using several appliances, such as functional removable appliance to modify dental and skeletal relationship, fixed orthodontic appliances with tipping and bodily movement or using jaw reposition by orthognathic surgery.Results : One of the effective appliance to reduce overjet, especially Class II malocclusion treatment is Twin Block Functional Appliances developed by Clark. Twin Block appliances is used for developing age children in certain time period to support mandibular growth. This appliance is easy to use, so the patient cooperativity can be maintained. Maximum treatment depends on children’s cooperativity. By using Twin Block functional appliance, we can observe that early treatment can be effective to reduce overjet, to change skeletal pattern, and to increase children psychology such as self-confidence by making aesthetic changes to their faces significantly.[B1] Conclusion : This appliances is made with 70o angle to occlusal plane. Maxillary arch lateral expansion can be achieved with expansion screw. Patient will be instructed to use the appliance for 24 hours a day.[B2]