A foldable bicycle has a rear frame, a folding assembly and a front frame. The rear frame has a seat tube, a bottom bracket, a rear fork and a rear wheel. The folding assembly is connected to the rear frame and has a supporting device, a rotating jacket and a locking device. The supporting device is connected to the bottom bracket and has a mounting bracket and a supporting element. The mounting bracket is connected to the bottom bracket. The connecting tube is pivotally connected to the mounting bracket. The extending tube is connected to the connecting tube. The rotating jacket is rotatably mounted around the extending tube. The locking device is connected to the rotating jacket and the seat tube of the rear frame. The front frame is connected to the folding assembly and has a top tube, a head tube, a front fork and a front wheel.