The invention relates to a mixer, and more particularly to an ultra wideband medium frequency double balanced mixer circuit. The circuit comprises a first Balun, a second Balun and a diode bridge formed by sequentially connecting anodes and cathodes of four diodes. A midpoint 1 and another midpoint 2 of the first Balun are separately grounded. A capacitor-resistor parallel resonance structure is connected between the midpoint 1 and another midpoint 2 of the first Balun. According to the ultra wideband medium frequency double balanced mixer circuit, the midpoint 1 is directly grounded, and the capacitor-resistor parallel resonance structure is introduced between the midpoint 1 and another midpoint 2, so that the impacts of the prior art are eliminated, the electrical performance of the mixer is improved, and the medium frequency bandwidth of the double balanced mixer is increased.