The tides, tidal currents and tidal prisms at Inchon Harbor are studied with recent data. The tides at Inchon Harbor is of semi-diurnal type having a spring range of 798cm and a phase age of 2 days. The monthly mean sea level at Inchon has a maximum at August and a minimum at January with a annual range of about 40cm. the tidal currents at Inchon Outer Harbor are of semi-diurnal type same as tides and nearly reversing type. The flood and ebb currents set north and south with a velocity of about 90-175 cm/sec and 120-225 cm/sec at spring tide and begin 0.2 hours after L.W. and 0.7 hours after H. W., respectively. Non-tidal currents flow southward with 10-20 cm/sec at west side of the stream and northward with 15-20 cm/sec at east side of the stream at Inchon Outer Harbor. The flood volume through the Inchon Outer Harbor fluctuates fortnightly from 590 10$^$6/㎥ spring tide to 260 10$^$6/㎥ at neap tide and ebb volume changes from 470 10$^$6/㎥ at spring tide to 200 10$^$6/㎥ at neap tide, respectively. The flow area along the channel to the Estuary of Yeomha is controlled by the tidal prism as expressed by A=1.14 10$^$-4/ P$^$0.966/