A self-oscillating mixer (SOM) that uses a six port microstrip power divider is presented in this article. The oscillation and mixing functions are executed using a pair of identical GaAs field effect transistors. The power division and combination of the RF and local oscillator (LO) signals involved in the operation are implemented using the six port network. The RF input port of the proposed SOM is totally isolated from the operation of the LO which is a desirable feature in many applications. The proposed structure can work as a stand-alone oscillator with a frequency of 4.71 GHz and a power level of 16.1 dBm. When fed with a RF signal, the proposed structure becomes a fully functional SOM exhibiting a conversion gain of 5.2 dBm. The simulation and measurement results of the proposed SOM are presented to validate the design concept. V C 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:269-276, 2015.