According to current art, high lift devices such as leading edge slats are essential during the takeoff and landing stages of large transport planes. Due to complexity of the mechanical positioning mechanism and complex geometry there are regions on the main wing which are exposed to the slat tip vortices. Under adverse conditions, the vortices degrade the exposed region of the wing performance which result in lower lift and higher drag. In this experimental study, an airfoil with leading edge slat was tested for performance enhancement of a thick airfoil section with and without operating active flow control system positioned at the 20% chord location. It was found that the slat improved the overall performance and that the active flow control alone can deliver similar performance gains as the slat for this type of wing section with achievable low actuator control authority. Part-span slat configurations, covering 1/3 and 2/3 span, were also tested. It was found that there are positive effects of the AFC on the airfoil three-dimensional flow field and that in principle, AFC can supplement, or even replace the slat-edge adverse effects altogether.