This study examines the performance of peak-clipped optical BPSK-SSB signal. The effectiveness of peak clipping for PAPR reduction and the degradation caused by peak clipping are numerically analyzed. PAPR of optical BPSK-SSB signal becomes high because of the peaky Hilbert-transformed signal component. PAPR improvement of 43.7% is attained by clipping the peaks of the Hilbert-transformed signal. Assessment of spectral degradation reveals that both waveform clipping and modulator nonlinearity contribute to sideband suppression degradation. Analyses of the 100-km transmitted signal results show that PAPR reduction by peak clipping alleviates the nonlinear phase shift caused by self-phase modulation (SPM), which produces a less degraded signal at the detector. Peak clipping can improve the SPM threshold of the studied system by 2.63 dB.