The effect of antimony concentration on the piezoelectric properties of (Na0.5K0.5)(0.945)Li0.055Nb1-xSbxO3 was examined for 0 <= x <= 0.1. The piezoelectric coefficients exhibited a maximum, d(33)=240 pC/N and d(31)=-82 pC/N at x=0.04, coinciding with the maximum of the grain size and the apparent density at x=0.04. The grain size, the apparent density, and the piezoelectric coefficients decreased with an increasing x at higher x likely due to the onset of a Sb-rich second phase. The weight fraction of the tetragonal phase increased with an increasing x to almost unity at x=0.1, likely also contributing to the decrease in the piezoelectric coefficients at higher x.