Crowded large space buildings are today becoming highly desirable facilities for communities, towns, and cities. Due to stricter health, safety requirements, and environmental effects, such buildings are of greater interest for research. The buildings are used for a variety of functions, including sporting, entertainment, and religious events. The Holy Mosque in Makkah Saudi Arabia is an excellent example of a crowded large space building with a maximum capacity reaching up to 2 million users, especially at the Hajj and Ramadan periods. Quite often, designer and facility managers of crowded large space buildings pay keen attention to normative and substantive (objective) safety, but research shows that perceived (subjective) safety which should also be important, is clear overlooked. To prove the significance of perceived safety, a theory has been adopted, which states that a reduction in perceived safety (PS) will negatively affect the user behaviour (UB) resulting in the occurrence of a disaster in crowded large size buildings. Initial research undertaken by the authors have identified 10 key factors affecting subjective safety in crowded large space buildings, this stage of the study is an empirical study to aimed at establishing how significant each factor affects PS and the effect of perceived safety on the UB in such types of buildings. The Holy Mosque was used as a case study. The research adopted the quantitative research methodology by collecting primary data using a group-administered questionnaire in electronic devices such as iPad from more than 1,940 Hajj pilgrims coming from 62 countries. This was analysed by SPSS and AMOS 22 for confirmatory factor analysis (CFA) and structural equation modeling (SEM) to test the interrelationships between the 10 identified factors and PS or between PS and UB through several hypotheses. The research has demonstrated that there is a significant influence on PS by most of the established factors and that PS has a significant influence on the behaviour of pilgrims in the Holy Mosque.