The crustal thickness and uppermost mantle P wave velocity at several seismic stations in Northwestern Turkey were estimated using the established travel time-distance relation method. The data suggest a flat layered crust of average thickness 28.4¿3.45 km with an average uppermost mantle P wave velocity of 8.05¿0.17 km/s. This is similar to results obtained for the North Aegean Sea and suggests a close structural link between the two areas.