Tunable resonant cavity enhanced detectors (RCED) have been realised for the mid-infrared (IR). The bottom mirror as well as the photodiode inside the cavity are based on narrow gap IV-VI materials and grown by molecular beam epitaxy (MBE) on Silicon substrate. The length of the cavity and therefore the resonance wavelengths can be adjusted continuously by a movable top mirror. We present measurements of such an RCED with a tuning range from 4.6 µm to 5.1 µm.