In this paper, a low-power Reed-Solomon (RS) decoder for STM-16 optical communications is presented. It mainly contains one (255,239) RS decoder and four 2 K-bit embedded memory for correcting the received codewords. Except the novel syndrome calculator reducing half the syndrome computations, our proposal also features a modified Berlekamp-Massey algorithm in the key equation solver and a terminated mechanism in the Chien search circuit. The (255,239) RS decoder is implemented by 0.25 μm CMOS 1P5M standard cells with gate counts of 32.9 K and area of 2.03 mm2. Simulation results show our approach can work successfully at the data rate of 2.5-Gbps and achieve 80% reduction of power dissipation on the average.