<p>This study investigates the impact of liquid sloshing on the efficiency of structural response control in a tuned liquid column damper (TLCD). While most research assumes that the free surface of the liquid remains flat and horizontal during oscillatory motion, real-world conditions cause the surface to become curved, exhibiting sloshing behavior. To account for this, a finite element model of the entire liquid domain within the TLCD is used. From the finite element model, sloshing-induced hydrodynamic forces acting on the TLCD walls are estimated. A numerical analysis is conducted on a single-degree-of-freedom structure with attached TLCD. The structure-TLCD system is subjected to both far- and near-field earthquake ground motions. The oscillatory frequency of the liquid in the TLCD is tuned to the natural frequency of the structure. Optimal TLCD design parameters are determined using the ‘<i>fminsearch</i>’ routine of MATLAB. The structural response reduction by the damper is obtained with and without considering the effect of liquid sloshing in the vertical limbs of the TLCD. The results reveal that non-consideration of the sloshing effect results in an overestimation of the control efficiency of the TLCD.</p>