A novel microstrip lowpass filter (LPF) with high selectivity and wide stopband is proposed in this letter.The proposed LPF consists of three compact microstrip resonant cells, two E-shaped feed-lines on the top layer and four defected ground structure (DGS) slots on the ground plane. The top layer LPF is designed to have a sharp roll-off characteristic, whereas the engineered DGS slots on the ground plane are used to reduce the passband ripples and extend the stopband bandwidth of the proposed LPF. A selectivity of 53.4 dB/GHz is achieved. The stopband with an attenuation level of 20 dB is obtained from 2.96 to 13.2 GHz. The filter is optimally designed, fabricated, and measured. Both simulated and measured results are presented, which show a good agreement between simulation and measurement.