The design of microwave planar quasi-elliptic dual-mode filter is presented in this paper. The filter's design includes a novel quasi-elliptic dual mode filter design realized by using stepped impedance dual mode resonator with source-load coupling to give passband characteristics of two transmission zeros beyond the passband. In contrast with an elliptic filter, a quasi-elliptic filter will allow us to adjust our transmission zeros to any desired finite frequency for more selectivity. The design gives a sharp cut-off response with significant size and complexity reduction which are critical in modern communication system applications that require remarkable filter performances. The filter has the center frequency of 1GHz and the passband bandwidth designed to be less than 5. The analysis and design of the filter are also presented with the simulated results to show the design feasibility. © 2011 IEEE.