This paper investigates the problem of decomposition with respect to outputs for Boolean control networks (BCNs). First, with the linear expression of BCNs and the matrix semi-tensor product, some algebraic equivalent conditions for the decomposition are obtained. Second, a necessary and sufficient graphical condition for the decomposition with respect to outputs is given. Third, an effective method is proposed to reduce the computational burden in the realization of the decomposition. Finally, some examples are addressed to validate the effectiveness of the proposed method.