In this paper, a decentralized formation control based on adaptive super-twisting algorithm (ASTA) is designed for a group of unicycle mobile robots. According to this approach, movements of robots are driven through a sequence of formation patterns. This control scheme increases robustness against unknown dynamics and disturbances, whose bounds are not required to be known. Furthermore, a high-order differentiator is designed to estimate unmeasurable signals, in order to implement the proposed controller. Finally, simulation results illustrate the effectiveness of the proposed control scheme.