We propose a multiple-subcarrier (MS) optical communication system using intensity modulation with direct detection (IM/DD) with peak reduction carriers (PRCs) to improve the power efficiency of IM/DD MS systems. The proposed system transmits L subcarriers referred to as PRCs among N subcarriers for the d.c. bias reduction so that the optical power is reduced. Since information bits are mapped onto each subcarrier other than PRCs independently, the information bits of each subcarrier can be detected independently and the error rate of the proposed system is unaffected by PRCs.