A foldable bicycle frame includes a rigid element connecting a head with a seat tube, a rear section of the frame, a coupler, and an intermediate seat tube. The front upper part of the rear section of the frame is pivotally connected to the intermediate seat tube. The front bottom part of the rear section of the frame is pivotally connected to the coupler. The other end of the coupler is pivotally connected to the rigid element. The intermediate seat tube is operable to be inserted into the seat tube while unfolding the frame.