This paper investigates navigational risks that local traffic exposes to transit passing vessels through Istanbul Strait. Risk analysis was performed at the South entrance area of the Istanbul Strait, where the local traffic is most congested. For this Purpose, the research area was created digitally and simulation studies were carried Out using ship handling Simulator which can imitate the effects of topographic features, vessel traffic and meteorological conditions. Furthermore, the results Of the Simulation were analyzed using Environmental Stress Model of Inoue (2000) which provides an opportunity to analyze vessel traffic risks quantitatively. As the result of the study, the danger that is exposed by the local traffic to the transit-ships was demonstrated and lie most dangerous spots in the research area were seized for further precautions.