In this paper, a new barrier function-based adaptive strategy is proposed for first order sliding mode controller. This strategy is applied to a class of first order disturbed systems whose disturbance is bounded with unknown boundary. The proposed barrier strategy can ensure the convergence of the output variable and maintain it in a predefined neighborhood of zero independent of the upper bound of the disturbance, without overestimating the control gain. (C) 2018 Elsevier Ltd. All rights reserved.