The impact of the urban heat island (UHI) effect on environmental and regional climate has been receiving wide attention in recent decades. Taiwan, especially Taipei (located in northern Taiwan), is experiencing a significant UHI effect due to its high population density and the uniqueness of the geographic structure. In order to evaluate the impacts of urbanization and UHI effect over northern Taiwan, a next generation mesoscale model, Weather Research and Forecasting (WRF) model coupled with the Noah land surface model and Urban Canopy model (UCM), was used to study this issue. By using the WRF-Noah-UCM model, it has significantly improved our simulation results for the prediction of the UHI effect, boundary layer development, and land sea breeze. Observations of weather stations and Lidar showed that the near surface air temperature was nearly 34-35 °C and the boundary layer height was nearly 1500 m around noon in Taipei on 17 June 2006. Around midnight, the air temperature ranged from 26 to 28 °C. Our model can predict well for boundary layer development during the daytime and the UHI effect in northern Taiwan. Sensitivity tests indicate that the anthropogenic heat (AH) plays an important role for the boundary layer development and UHI intensity in the Taipei area, especially during nighttime and early morning. When we increase AH by 100 W m-2 in the model, the average surface temperature could increase nearly 0.3 °C in Taipei. Furthermore, we found the UHI effect also has a significant impact on land sea circulation. It could enhance the sea breeze in the daytime and weaken the land breeze during the nighttime and hence had a significant impact on the air pollution diffusion in northern Taiwan.