Four-wave mixing (FWM) is an important mechanism for frequency conversion and fast optical switching in all-optical communication networks. In this paper, we demonstrate that microring resonator filters can generate significant conversion efficiency with sub-millimeter physical size. Microresonator based filters not only have high finesse, which can enhance nonlinear efficiency, but also have periodic passbands, which satisfy the phase matching condition of FWM automatically. Non-degenerate FWM in direct-coupled ring resonator (DCRR) filters and ring-based Mach-Zehnder interferometers (RMZI) is studied in this paper. Both structures provide greater than 10% conversion efficiency (defined by the converted intensity divided by the initial signal intensity) with low values of n2*Ip, where n2 is the nonlinear refractive index and Ip is the initial pump intensity; the DCRR allows greater frequency conversion bandwidth within the filter passband. We also compare the efficiency of the ring-based filters and a straight waveguide with the same effective length. We thus demonstrate that ring-based filters are effective devices for on-chip wavelength conversion for WDM network.