Reconfigurable optical add/drop multiplexers (R-OADMs) are indispensable devices in wavelength division multiplexing (WDM) network systems, since they can be used for dynamically wavelength routing and for replacing any failed OADM unit. Here, we propose a photonic integrated R-OADM device based on silicon photonic crystal (PhC) slab waveguides, which is controlled through thermo-optic effect. The R-OADM device was composed of a tunable wavelength multiplexer/demultiplexer and a 2×2 optical switch, which were both formed with Mach-Zehnder interferometers (MZIs). The device was compact with a net footprint of 500 μm × 140 μm, excluding its electrode pads. The dropping central wavelength of the R-OADM can be tuned through thermo-optic effect, and the output port of the drop signal can be selected between the THROUGH and DROP ports with the 2×2 optical switch. A maximum 10.8 nm dropping wavelength tuning was obtained with a heating power of 0.9 W. The 3-dB channel-dropping bandwidth was 5 nm and the extinction ratio at the dropping wavelength for the port THROUGH was as high as 40 dB. The tuning response speed was about 100 μsec.