A triband bandpass filter is proposed and designed in this paper. By employing CQ topology and the defected ground structure (DGS), eight transmission zeros (TZs) are generated and high frequency selectivity and interband isolation are obtained. The twosection half wavelength stepped impendence resonators (SIRs) are carefully designed as common resonators which resonate at the first three passband simultaneously, the quarter wavelength resonators (QWRs) that resonate at the first and third passband respectively are added to assemble quadruplet filters. Meanwhile, the defected ground structure (DGS) is etched on ground surface to adjust the coupling coefficients flexibly for specified demands. The triband bandpass filter operating at 2.4, 3.4, and 5.5 GHz simultaneously is designed, fabricated and measured. The good agreement between measured and simulated results verifies the the reliability of the proposed design method.