As air-traffic control (ATC) services are provided for the purpose of achieving flight safety and efficient aircraft operations, the role of air-traffic controllers in the aviation system is vital. Since the accident rates caused by human error have been increasing, major aviation institutes worldwide are actively conducting research on the human factors affecting controllers. Among human factors in aviation, situation awareness (SA) and workload have been at the center of many research activities for years. Also, many people have expressed an interest in how these two constructs relate to each other. In this article, the relations between controllers' SA and workload were explored under different taskload conditions. An experiment that included ATC simulation to measure the controller's SA and workload at various air-traffic situations was conducted. Based on the results of this study, the measures to keep the controller's SA and workload at a manageable level and the effective training programs can be explored.