This study investigated the characteristics of mud transport at the ship channel of Miike Port in Ariake Bay, based on field observations and numerical simulations. The findings are as follows: (1) The Suspended Solid (SS) transported from the outside of the port at flood tide is settled down in the channel due to small current, but SS transport is little at ebb tide because of low suspension. (2) The actual settling velocity of the SS in the channel is possibly lager than that in the technical literatures on another part of Ariake Bay. (3) A new observation technique by a slanting radiation of acoustic beams from H-ADCP has clearly confirmed that wave condition in rough sea much affects SS transport into the channel