The present invention is a convertible uni-bicycle, wherein the front end of a bike frame is connected to the outer wall of a head tube using a dismountable structure, and the top end of the head tube is connected to a handlebar using a dismountable structure. The handlebar disposes a brake lever which is connected to an upper brake cable, and the upper brake cable is interconnected to a lower brake cable using a jointing structure. Then, the top end of the bike frame mid-section is connected to a seat post using a dismountable structure, and the bottom end of the bike frame mid-section disposes a driving mechanism which is installed with two dismountable pedals. Thus, the present invention provides a means for the user to convert bicycle into unicycle through easy steps.