Many boring investigations were achieved in Youngjong-North tidal flat to construct the Incheon International Airport Expressway. Vertical sedimentary profile of this tidal flat has been studied by analyzing these boring data. The deposits of Youngjong-North tidal flat are about 30 meters thick, and the sedimentary layers consist of basal gravel, lower mud, middle silt, middle mud, and upper silt layers in ascending order. Semi-consolidated and oxidized belt with yellowish brown color, which appears above or within middle mud layer, exists in $-3{sim}-5$ meters altitude. There are some stratigraphical problems to admit the top surface of this oxidized belt as the unconformity surface between Holocene and Pre-Holocene tidal flat deposit.