This paper describes the experimental investigation of tidal exchange ratio by use of Tokyo Bay model.
　There are several definitions of tidal exchange ratio and these are different from model to model respectively. The difference among them are explained by use of the figure.
　From the experiments, pattern of tidal current of Tokyo Bay are characterized that the outflow is predominant in the kannonzaki side of the bay entrance section, on the other hand the inflow is predominant in the Futtu side of same section. The circulation due to tidal current promotes the exchange of bay and ocean water.
　The methods employed in this investigation of tidal exchange are Hayami's model and Parker's model. As a consequence, it is estimated that the tidal exchange ratio at entrance section (Kannonzaki to Futtu) of Tokyo Bay is several percent or so.
　Exchange ratio of Box model is overestimated than other models.