In this paper, in order to develop excellent composition ceramics for a piezoelectric energy- harvesting device, we synthesized 0.99(Na0.52 K0.443 Li0.037)(Nb0.883 Sb0.08 Ta0.037)O3 + 0.01(Sr0.95 Ca0.05)TiO3 + 0.3 wt% Bi2O3 + 0.3 wt% Fe2O3 + 0.3 wt% CuO (abbreviated as NKN-SCT) ceramics with different sintering times, using the ordinary solid-state reaction method. The effect of sintering time on the microstructure and piezoelectric properties was investigated. The ceramics with the sintering time of 7 h have the optimum values of the piezoelectric constant (d33), piezoelectric voltage constant (g33), planar piezoelectric coupling coefficient (kp), mechanical quality factor (Qm), and dielectric constant (εr): d33= 314 [pC/N], g33= 20.07 [10-3 mV/N], kp = 0.442, Qm = 93, εr = 1,768, all being suitable for a piezoelectric energy-harvesting device.