Thos case report described the skeletal and dental changes contributing to class II skeletal with mandibula retrognatism correction with Twin Blocks appliance. Cephalometric evaluation were compare between pre-treatment and after eight month treatment wearing Twin Blocks appliance at an 8 year, 1 month old girl patient. This short-term cephalometric study indicates that after eight month treatment with Twin Blocks appliance, the overjet reduces 3 mm correction of the first molar permanent from class II Angle (cusp to fossa) to class II Angle (cusp to cusp) and lengthening the mandible.