This paper addresses the problem of stabilizing the motion of an aerial manipulator composed of a Quadrotor and a manipulator with two degrees of freedom (2 dof). The dynamic modeling of an aerial manipulator, like the one presented in this paper, shows that there is a strong physical coupling between the dynamics of the UAV and the manipulator arm. This coupling, plus external perturbations (e.g. wind gusts), considerably affect the stability of the drone's motion in flight which, consequently, affects the desired accuracy of the end effector with respect to its final task. To overcome this problem, we propose in this paper an approach based on an adaptive gain sliding mode control, a priory without the need to know its bounds, and to make the gain as small as possible but sufficient to overcome these disturbances due to both the arm motion and external uncertainties. The effectiveness of the controller and its robustness against noise are verified and analyzed using MATLAB/SIMULINK.