This letter proposes a scheme for the format conversion of on-off keying (OOK) signal to quadrature phase-shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM) signals via cross-phase modulation (XPM) in a semiconductor optical amplifier (SOA). Theoretical and experimental analyses of the format conversion scheme are conducted to validate its feasibility. The phase changing is obtained because of the XPM in the SOA. The QPSK and 16QAM signals are converted from the OOK signal. The performance of the 10 Gb/s format conversion system is evaluated and discussed. The receiver sensitivities of the converted QPSK and 16QAM signals after detection are -27.25 and -23.5 dBm, respectively, at a bit error rate (BER) of 10-9.