The derivation and implementation of the natural switching surfaces (NSS) considering parametric uncertainties for a flyback converter operating at boundary conduction mode (BCM) is the main focus of this paper. The NSS presents many benefits for the control of non-linear systems; for example fast transient response under load-changing conditions. However, the performance considerable worsens when real parameters of the converter are slightly different from the designed ones. Therefore, a novel control strategy that considers the effect of parameter uncertainties is presented. This control law can estimate and adapt the control trajectories in one switching action to obtain excellent performances even under extreme parameter uncertainties. The analytical derivation of the proposed adaptive switching surfaces are presented.