This research was aimed to classify the climatic conditions of different locations in Thailand into zones of relatively similar ambient conditions. This classification is extremely useful to the building design for a wide range of objectives such as energy conservation, residential thermal comfort, outdoor design conditions, etc. The data of 18 years of ambient air temperature and relative humidity recorded by the Meteorological Department of Thailand from the 73 observation stations in the kingdom were studied and analyzed by a simple statistical methodology. To this end, the significant level defined as the number of days in a class interval divided by the total number of days of occurrence was used. Thus, only data with more than or equal to 2.5% significant level values were used to develop the climatic zones of Thailand map. Two maps are proposed: the first displays three dry bulb temperature zones, named T1, T2 and T3 with the following interval ranges 12-38, 16-38 and 20-38 degreesC, respectively. The second map displays four relative humidity zones, named H1, H2, H3 and H4 with the following interval ranges 30-100, 41-100, 50-100 and 59-100%. The frontiers of the zones were adjusted according to the provinces' delimitation. The zones coincide well with the existing geographical location and the seasonal variation demonstrating that a prediction made by the consideration of climatic conditions could be sufficient for conducting good studies and design.