In this paper, a mode composite coplanar waveguide (MCCPW) is proposed and studied. The MCCPW can be regarded as a combination of a quasi-coplanar waveguide and a substrate integrated waveguide (SIW). In this composite structure, the center conductor of the quasi-coplanar waveguide serves as the SIW supporting TE10 mode, while the TEM mode operates in the quasi-coplanar waveguide part. The characteristics and design method of the MCCPW are analyzed and illustrated in this work. The MCCPW is fabricated together with two transition structures to demonstrate its integration capability further with other planar circuits. The MCCPW is a single layer structure, and it has the advantages of joint structure and mode composition, which make it a possible solution for multifunction and multiband application systems. The measured and the simulated results agree well with each other, and good transition performances are achieved.