Aiming at the problems of big passband insertion loss and poor outofband rejection of wideband filter operating at microwave band, a novel ultrawide band microwave filter with defected ground structure(DGS) and defected microstrip structure(DMS),which are of slowwave effect and singlepole bandreject characteristic,was designed in this paper. The modelling and simulation of the filter have been carried out by using the electromagnetic simulation software HFSS and the devices have been fabricated by the PCB process. The measured results agree well with the simulation ones. The proposed filter has an insertion loss of better than 1.64 dB and a return loss of better than 13.93 dB;a fractional bandwidth of 100.45% are achieved, the passband range is from 2.75 to 8.3 GHz; besides, the stopband attenuation is up to -10 dB. The filter shows a desired performance with a compact size.