A microwave spark plug (1) for injecting microwave energy into the combustion chamber 18 of the engine, it includes an elongated housing (2), wherein the housing has an elongate cavity 10 for forming the hollow conductor in the interior of the housing comprises the housing (2) comprises a microwave window (8) arranged at a first end of the cavity (10) within said microwave window, wherein the hollow conductor (10) to said combustion chamber (18) a sealed, said cavity (10) said microwave window (8) and at a second end facing saw arrangement includes a connection piece (4) for the high-frequency supply conductor, said connector piece (4), said microwave window high frequency comprises an outlet cross-sectional shape with different high frequency inflow cross-section-shaped part (7), the high frequency outlet cross-sectional shape at the second end of the hollow conductor from the high frequency inlet cross-section portion at the first end of the hollow conductor formed on part to the transition portion is formed in a continuous. It said microwave spark plug is formed such that tightening the screw into the typical borehole for a spark plug is securely inject microwave energy into the combustion chamber of the internal combustion engine.