Along with the global concern of the Environmental Assessment of Buildings, the Kingdom of Saudi Arabia (KSA) had recently used its system, Mostadam, to provide a suitable method to assess its buildings environmentally. Nevertheless, Mostadam still cannot be used for all Saudi Arabia regions without having misleading results, which is due to its various internal regions with their various characteristics. Taif city has its unique environmental characteristics, which affect all the environmental buildings’ assessment fields. This research aimed to adjust the Indoor Environmental Quality (IEQ) field of Mostadam according to Taif characteristics. The research analyzed Taif characteristics that have an impact on the IEQ field, which are mainly related to the occupants’ different comfort needs and health requirements. Then, according to an analytical methods, authors proposed some changes to adjust Mostadam IEQ field according to these characteristics. The research resulted in an obvious difference between the resulted IEQ items weights and formulation versus the origin one of Mostadam, which proves the need for such adjustment to achieve a fair and trusted assessment to achieve the utmost credible assessment results when assessing buildings environmentally in Taif. It is recommended to adjust other assessment fields similarly later on, and then globally