Source sensitivities are useful for identifying key contributors to ambient pollutant concentrations and for predicting the effectiveness of reductions in precursor emissions. In this study, we analyzed the sensitivities of surface ozone concentrations in major coastal regions of Japan using air quality simulations. The targeted coastal regions include areas located 0–25 km and 25–50 km from the coastlines of the Seto Inland Sea, Osaka Bay, Ise Bay, and Tokyo Bay. For long-term mean surface ozone concentrations, sensitivities to transport from outside Asia and to background methane chemistry are dominant. Spatial discrepancies driven by differences in ozone formation regimes are evident in areas with high precursor emissions and large associated sensitivities. Sensitivities to vehicles, large combustion sources, and ships—which primarily emit NOx in coastal regions—are larger in areas located 25–50 km from the coastlines, whereas sensitivities to biogenic VOCs, which are mainly emitted in rural areas, as well as fugitive VOCs, are larger in areas located 0–25 km from the coastlines. For short-term high surface ozone concentrations, sensitivities to transport from outside Asia and to background methane chemistry are relatively smaller. Sensitivities to both NOx and VOC sources are generally larger in areas located 0–25 km than in areas located 25–50 km from the coastlines, indicating that anthropogenic NOx and VOC sources drive short-term high surface ozone concentrations in populated coastal areas. These results highlight the importance of considering spatial and temporal differences in sensitivities when developing effective strategies to suppress surface ozone concentrations.