We describe relationships between dissolved oxygen (DO) and vertical mixing rate (Kz) based on in-situ survey data in Tokyo Bay. Seven field observations were carried out in the period, July 2011- March 2012, using the micro-structure profiler to simultaneously measure high-resolution profiles of shear, temperature, salinity, fluorescence and DO. The observed data showed that hypoxic water mass occurred in the middle layer at the end of August. The hypoxic water was located in the region with Kz ‹ 10-5 m2/s, which was distributed between the surface mixing layer and the bottom boundary. The profile data also indicated that the intrusion of the bottom high-salinity water from the bay mouth to the bay head was an important role in the recovery process of DO in Tokyo Bay.