In the design of bridges, it is important to consider the thermal stresses induced by the non-linear temperature distribution as well as the variation of effective temperature in the bridge deck. To cope with this, design temperature profiles are provided by design codes, which are normally based on extensive research work. This paper presents the results of a comprehensive investigation on the thermal behaviour of bridges in Hong Kong with special emphasis on composite bridges. The temperature distribution in bridges depends primarily on the solar radiation, ambient air temperature and wind speed in the vicinity. Apart from data of the meteorological factors, good estimates of the thermal properties of material and the film coefficients are necessary for the prediction of temperature distribution. The design temperature profiles for various types of composite bridge deck with bituminous surfacing and concrete slab of different thicknesses are proposed. The factors affecting the design effective temperature are also reviewed and suitable values for Hong Kong are proposed. Results are compared with recommendations of the current local code. The method facilitates the development of site-specific temperature profiles for code documents, and it can also be applied to create zoning maps for temperature loading for large countries where there are great climatic differences.