A thermally conductive composite consisting of polycarbonate (PC) resin and boron nitride (BN) was prepared by injection molding method. The effects of size and content of BN particles, preparation process of the composite, and the dispersion state of BN on the thermal and mechanical properties of the composites were investigated. The result showed that thermal conductivity of BN/PC composite prepared by the proposed was much higher than that of BN/PC composite prepared by either melting method or powder method. In addition, the thermal conductivity of the composites could be improved by increasing the BN particle size, but the tensile strength would be decreased. With the increasing content of BN particles, the thermal conductivity could be increased accordingly. Meanwhile, the tensile strength first increased and then decreased. When the content of BN was increased to 5 wt%, the tensile strength can reach the maximum value of 65.14 MPa. The thermal properties of the composites prepared by BN/PC solution and PC beads were better than those of BN/PC composites.