"This article presents the effect of fractured zones on subsea tunnels. Generally, a subsea tunnel is designed to support high water pressure so that the hydraulic condition is of fundamental interest. In cases where fractured zones exist along the tunnel route, attention should be paid to it at the design stage. However, there is not much information about the hydraulic influences on the fractured zones. Pore water pressure and inflow rates are the main hydraulic factors to be considered in the design. In this article, the hydraulic effects on the fractured zones of a subsea tunnel under construction and during operation have been investigated using a numerical method and small scale model tests. The Vardø tunnel, which is a subsea tunnel in Norway (Grønhaug and Lynnegerg, 1984), is used for the numerical modeling. Based on the analysis results, the significance of fractured zones in subsea tunnels is identified."