Abstract: An atrium is a type of space which is physically shaped as an enclosure inside the building. It is modified from courtyard or an opened enclosure in middle of the building. This research is conducted to identify the effect of atrium size to the air movement velocity rate and its distribution through the rooms in a square-shaped natural-ventilated high rise building. https://www.diegojavierfares.com/mega-pick-Jessamine-Orange-Peel-Monrovia-great-pick/