Optical coherence tomography (OCT) is a contactless and non-invasive imaging technique. Due to the high resolution of some 10 μm and the penetration depth of 1-2 mm in scattering tissue, OCT closes the gap between microscopy and sonography. Here, we present a GRIN-based endoscopic OCT (eOCT) system for middle ear diagnostics. EOCT combines the benefit of endoscopic imaging and the advantage of morphological and functional investigation of the tympanic membrane (TM). The eOCT system has a working distance of 10 mm, which results in a field-of-view of 10 mm. This allows a full three-dimensional visualization of the TM and surrounding tissue. In addition, the oscillation of the TM can be measured spatially resolved and in the frequency range between 500 Hz and 5000 Hz with 125 Hz resolution, which is realized by phase-resolved Doppler-OCT. First clinical results are demonstrated for one selected cases, a middle ear effusion.