A foldable bicycle frame includes top and bottom connecting bars respectively pivotally connected between front and rear top tubes of the bicycle, a plurality of springs supported between the top and bottom connecting bars for pushing the top and bottom connecting bars vertically away from each other for allowing the front top tube and the rear top tube to be turned relative to each other between an operative position and a non-operative position, and a locking mechanism controlled by a locking lever to lock the top connecting bar and the bottom connecting bar in a position where the front top tube and the rear top tube aren't movable relative to each other.