In this study, coplanar waveguide (CPW) stop-band filters based on open split ring resonators (OSRRs) are presented for the first time. The filters consist on a cascade of transmission line sections, acting as impedance inverters, alternating with shunt connected OSRRs. An order-3 Butterworth stop-band filter is presented as an illustrative example. The second part of the study deals with the application of these stop-band filters to improve the out-of-band rejection (through spurious suppression) of wideband band-pass filters implemented by means of open complementary split ring resonators (OCSRRs). The combination of OCSRRs (the complementary counterparts of OSRRs) and OSRRs for the design of CPW band-pass filters is used for the first time in the proposed prototype device example. The achieved results are promising and are indicative of the possibilities of these electrically small open resonators (OSRRs and OCSRRs). © 2010 The Institution of Engineering and Technology.