The interactions of the sea breeze with urban heat islands (UHI) are examined with use of a two-dimensional numerical model. The strength of the interaction depends on the intensity of the sea breeze, the intensity of the heat island circulation that develops over the inland side of the urban area, and the penetrating speed of the sea breeze. These factors are basically controlled by three characteristics of the urban area-the size or width, the distance from the sea, and the intensity of the UHI