Ancient Messene, Greece, was founded by Epaminondas in 369 B.C. Kumamoto University Architectural Mission to Greece has surveyed, since 2007, the architectural remains of the theater including more than a hundred blocks from walls, columns, etc., in order to reconstruct its form of Roman period. The authors analyzed remains and blocks in detail and tried to reconstruct the cavea in the last phase from the 1st to 3rd century A.D. We have reached conclusion that tha cavea was separated in 3 parts with 2 diazoma. The lower and middle cavea were separated into 11 and the upper cavea into 16.