<p>Force control merged with motion control represent the fundamental low level requirements for the most complex tasks to be performed by any robot. In particular, robust motion and force controllers allow robots to deal with real-world uncertainties among other disturbances. In this paper, an admittance-based force controller using the Active Disturbance Rejection Control approach is proposed, which allows to perform robot force control without a force sensor. In addition, a theoretical synthesis of the control law including an extended state observer for the estimation of the robot–surface force interaction and their formal stability analysis is presented. The validation of the proposal is depicted by numerical simulations using the dynamical model of a two degrees of freedom robot manipulator, for both a constant and a time-varying force control tasks with an unknown curved surface, while considering joint measurement noise and force sensors noise and an external disturbance force.</p>