Cases with bilateral posterior crossbite usually have skeletal discrepancy. The timing of treatment of bilateral posterior crossbite combined with functional shift is better to start earlier. This article presents a girl, aged 9 years and 6 months, with palatal arch constriction resulting in bilateral posterior crossbite and midline deviation. Through the use of rapid palatal expansion (RPE) appliance, the posterior crossbite had been successfully corrected. Normal occlusion has been obtained after three years follow-up.