Recent studies carried out by the Hong Kong Observatory show that the rising trends of air temperature in Hong Kong are influenced by both the global warming due to enhanced greenhouse effect and the high density urban development in Hong Kong. Apart from temperature, urbanization also brings about obvious d ifferences between the urban and rural areas in respect of relative humidity. The scope of the present study includes the selection of representative urban an d rural meteorological stations in Hong Kong so that the temperature difference between those chosen urban and rural stations can be utilized to quantify the ef fect of urbanization. By making use of some 20 years’ hourly temperatures and relative humidity data, this study preliminarily compared the diurnal variations and seasonal variations of the differences in temperatures an d relative humidity between urban and rural stations, and try to analyze the rel ationship between these differences and urbanization.