This study presents a sliding mode-based active disturbance rejection control (SMADRC) scheme for a steer-by-wire (SbW) system in road vehicles. First, a plant model that describes the mechanical dynamics of the SbW system is elaborated, where the viscous friction and the self-aligning torque are regarded as external disturbances. Second, the design of SMADRC is exposited, in which a non-linear extended state observer is utilised to estimate the non-linearities existing in the plant model, and a sliding mode control component is used to cope with the effect of the non-linearities and guarantee the control robustness against system uncertainties and varying road conditions. Finally, experimental results are shown to demonstrate the superiority of the designed SMADRC in comparison with a conventional sliding mode controller and a PD-based active disturbance rejection controller (PDADRC).