Dimensions (length, breadth and thickness) of carbonized rice grains excavated from 12 archeological sites were measured to investigate the origin of ancient Japanese rice . The ages of rice grains excavated were from the late Jomon to the Yayoi eras (from c.500 B.C. to c.300 A.D.). The excavation sites were located in the northern part of Kyushu, Japan. The 13 different materials from 12 excavations were analyzed for variations of the grain dimensions and were compared with those of 16 modern rice cultivars. The twelve sites were located in three geographical regions: three sites in the north-western Kyushu sea-shore region facing the Sea of Genkai, seven sites in the Chikushi alluvial plain region, and one of other two sites in the northern inland and the north-eastern sea-shore facing the Sea of Suo. The oldest sites were located in the north-western Kyushu sea-shore region. About 100 grains randomly sampled from the large masses excavated were measured using scaled photographs. In the cases where fewer than 180 grains were excavated, all available grains were measured. Results are as follows: 1.) The lengths of grains from the three sites in the northwestern efyushu sea-shore region were all shorter than those from the other nine sites.