Change of M₂ tide and tidal current due to the reclamation in Tokyo Bay is investigated using a three-dimensional numerical model. The sea surface area and volume of Tokyo Bay decreased by 25% and 8%, respectively, from 1923 to 1983 due to the reclamation. As a result, M₂ tidal amplitude in the bay and its water exchange volume across the bay mouth decreased by 8% and 35%, respectively. The surface sediment around the mouth of Tokyo Bay changed from sand to silt due to the decrease of tidal current amplitude there.