We investigated the effect of excess CuO on the sintering behavior, ferroelectric, and piezoelectric properties of lead-free $Bi_{0.5}(Na_{0.82}K_{0.18})_{0.5}TiO_3$ (BNKT) ceramics. The addition of excess CuO was found to greatly contribute to the densification and grain growth, however, excess CuO over 3 mol% was precipitated at grain boundaries after sintering. BNKT with 1~2 mol% CuO in excess sintered at $975^{circ}C$ showed piezoelectric properties comparable to those of unmodified BNKT sintered at $1,175^{circ}C$. These results seem meaningful for its application to low cost multilayer actuators (MLAs) because low firing ceramics make it possible to apply less expensive base metals to the inner electrode of MLAs.