GPS/Acoustic seafloor geodetic observation played a key role to estimate the slip distribution of the 2011 giant Tohoku-oki earthquake. After the event, seismic coupling near the trench axis has been a focus to understand how such a huge earthquake occurs in a subduction zone. Observation of postseimic deformation is another and urgent task required in the Japan Trench. In order to realize these observations, we have newly installed 20 GPS/A observation sites extending some 400 km along the Japan Trench in September 2012. Precision acoustic transponders were newly developed to cope with the following three requirements: (1) observation on the deep seafloor, (2) compatibility among three institutions in Japan, and (3) observation for ten years.