Abstract: A new spur-line defected ground structure (DGS) was designed, which was realized by etching in bottom-layer of the substrate. Meanwhile, a novel ultra-wide stopband low-pass filter with the spur-line DGS was developed, which composed of two spur-line DGS structures and the high/low impedance microstrip transmission line. It achieved the performance of wide stopband with miniaturization in structure. The following data were obtained from the simulation. The 3 dB cutoff frequency is 2.87 GHz, S₁₁ in pass-band are less than -20 dB, the stopband under the -20 dB is from 3.5 GHz to 20.3 GHz that is approximately 8.4 times of the cutoff frequency and the second, third or higher order harmonic response is effectively inhibited. Compared to the traditional DGS, the stopband of the spur-line DGS is broadened by 28% and, when the attenuation pole keeps the same, the occupied area of the spur-line DGS is decreased by 74%. The LPF has the property of compact, low insertion loss and wide stopband. Furthermore, the simulation results agree with practical measurement.