The present invention relates to an environmentally friendly foaming type buoy which: minimizes the occurrence of environmental pollution by being made of expandable polypropylene, an environmentally friendly material； minimizes the degradation of buoyancy since water is not absorbed well； reduces wear and tear relatively with improved durability； and enables a partial replacement as two bodies are joined together to form one buoy. The buoy of the present invention includes: a semicircular body of a semi-cylindrical shape which is formed with an expandable polypropylene material, has a semicircular surface in a semicircular shape with flat upper and lower surfaces, has a vertical surface in the front surface, and has a round surface formed on the outer circumference at both sides of the vertical surface； a plurality of coupling grooves which are formed concavely in a semi-cylindrical shape on the vertical surface and are formed to be separated at the same width； coupling jaws which have a semicircular shape, are formed on the vertical surface at one side of the coupling grooves, are formed to protrude at the same width and length as the coupling grooves, and are formed in the same number as the number of the coupling grooves； upper and lower surface grooves which are formed along the upper surface of the semicircular surface at the center of the upper and lower ends of the vertical surface； a vertical groove which is vertically formed on the round surface so that end parts of the upper and lower surface grooves are connected to each other； a round groove which is formed along the round surface at the center of both side ends of the vertical surface； and a pair of auxiliary vertical grooves which is formed to be vertical to the round surface between the vertical grooves and at each of both side ends of the vertical surface, and is formed to be symmetrical mutually. The two semicircular bodies are inverted to form a cylindrical body while the vertical surfaces are in
