Mineral phase analysis of ancient ceramics carried out by neutron diffraction yields complementary information to X-ray diffraction analysis. Since neutrons are highly penetrating, neutron diffraction in general allows non-destructive investigations of bulk samples rather than of surface layers or powdered material. This means complete, intact specimens can be studied. A time-of-flight (TOF) neutron diffractometer offers additional advantages considering experimental set-up, accommodation of large objects and data collection times. First test measurements with respect to archaeometric applications have been performed on different fragments of medieval Rhenish pottery using the TOF neutron diffractometer ROTAX at the spallation source ISIS, U.K. Phase fractions obtained from a Rhenish stoneware jar fragment compare well with those from a powder sample prepared from the same fragment. This finding indicates that reliable results can be obtained by illuminating a large piece or even a complete ceramic object without causing damage.