A wideband bandpass filter (WBPF) with excellent selectivity is proposed. An equivalent circuit model of the new complementary split-ring resonator (CSRR)-based resonator with good wideband response is presented. A WBPF with strong passband selectivity and wide stopband can be achieved by the new resonators with a proper coupled scheme using the eighth-wavelength (λ/8) directly coupled parallel microstrip-lines. Specifically, the filter exhibits a competitive attenuation slope of 262.2 and 75.9 dB/GHz in the lower and upper passband transitions, respectively.