A bone expandable device comprises two expanding members, a retractable member and a fastener. The two expanding members are joined together for forming a cavity therebetween, each the expanding member includes two flexible parts and a fixed part. The two flexible parts are connected to the fixed part separately, and each the flexible part can be bent from the fixed part. The retractable member is disposed in the cavity and includes a first part and a second part. The first part is movably sleeved on the second part, and a length of the retractable member can be adjusted by moving the first part or the second part. The fastener is for fastening the two expanding members together. When the length of the retractable member is increasing, the two opposite ends of the retractable member would push against the four flexible parts to expand the flexible parts outwardly from the cavity.
