The roofing tiles excavated at the site of the Taga castle, and the Hinodeyama kilns in the Miyagi prefecture which belong to the 8-10th centuries were found by Mössbauer spectroscopy to be rich in Fe₂+. To find the firing temperature of these tiles two samples of clay, taken from the site near the Hinodeyama kiln and another different site far from the above kiln, were fired in a reducing atmosphere at various temperatures up to 1300°C, and the Mössbauer effects were studied. Based on the comparison of these data with those of the roofing tiles excavated, the firing temperature of the roofing tiles was estimated to be 800-1000°C. -- AATA