Sliding surface design for nonlinear dynamical systems is a non-standard procedure if a linear sliding surface is not preferred for a well-performance controller application. Nonlinear sliding surface design, on the other hand, may become very complicated since the stability of the dynamical system on the designed sliding surface should be guaranteed. In this paper, a method is introduced for sliding surface design for a class of nonlinear systems. The proposed method uses the idea of Model Reference Adaptive Control (MRAC) and extends the idea to Model Reference Adaptive Sliding Surface (MRASS) design. For the nonlinear dynamical system, the methodology combines State Dependent Riccati Equation (SDRE) based Sliding Mode Control (SMC) with MRAC design. Within this context, a sliding surface is generated for the given nonlinear plant dynamics from a reference sliding surface by designing an adaptation mechanism. Adaptive sliding surface is then used for the sliding mode controller for the nonlinear plant. The design approach is illustrated via nonlinear dynamic model of a three-degree of freedom (3 DOF) helicopter model such that given elevation and travel commands are tracked. The simulation results are given to illustrate the proposed controller approach.