A novel super-twisting adaptive sliding mode control law is derived using Lyapunov function technique. The both drift uncertain term and multiplicative perturbation are assumed to be bounded with unknown boundaries. The proposed approach consists in using dynamically adapted control gains that ensure the establishment, in a finite time, of a real second order sliding mode. The efficacy of the proposed super-twisting control algorithm is evaluated through its application to position control of an electropneumatic actuator.