The complexity of high rise buildings poses challenges in the event of evacuation. The multiple floors of staircases, longer egress times and large number of tenants determine the success of a complete evacuation. Most high rise buildings are well equipped with state-of-the-art safety systems. Nevertheless, untoward disasters can still occur, ranging from fires to terrorist attacks. The readiness of tenants is an area of importance as this can delay the overall course of evacuation. Identifying the causes of common delay of tenants is elemental to continuously improve evacuation rate in the event of emergencies. In view of the increased number of terrorist attacks globally in recent years, high rise building is consistently on alert as it is usually a prime target. Therefore, carrying out evacuation drill is indeed paramount to emergency preparedness. Series of full scale and functional evacuation drills are conducted at the highest twin towers in the world, PETRONAS Twin Towers (PeTT) and Tower 3. Furthermore, PeTT include various type of businesses and tenants e.g. offices, shopping mall, large underground parking bay, as well as recreational and leisure facilities. A study to look into the tenants’ behaviours was carried out in concurrence with the evacuation drill. The purpose of the study is to identify the common behaviours that contributed to the delay of the overall evacuation time. Information pertaining to the common behaviours were gathered through observation and post-mortem findings. The information obtained from this study is necessary for PeTT to continuously improve its emergency response preparedness. The series of drills are also carried out to test the Business Interruption and Continuity preparedness, e.g. activation and mobilisation of Business Continuity Teams (BCT), activation of Alternate Work Site (AWS), readiness of ICT, as well as the response time in order to reactivate the critical business functions. This paper will focus on the study conducted based on the emergency evacuation exercise carried out on 10th July 2017, mainly on the behaviours of the tenants.