This paper discusses the effect of the signal pulse waveform on in-line optical amplifier transmission. Under a simple assumption for pulse width evolution along the line, the theoretical expressions of the received signal and noise levels are derived in terms of the initial signal waveform and the receiver response. Numerical analysis of pulse propagation taking fiber dispersion and nonlinearity into account is also carried out to evaluate signal waveform degradation and signal-to-noise ratio characteristics. The results of the theoretical analysis and those of the numerical analysis exhibit good agreement. The width and sharpness of the signal pulse launched from the transmitter are related, through the dispersion length and the nonlinear length, with the eye opening penalty which is proportional to the square of the transmission distance. It is also clarified that these quantities determine the proportionality coefficient of the square characteristics. Signal waveform distortion changes not only the received signal level but also the noise level, both of which affect the signal-to-noise ratio. A large width of the launched signal pulse alleviates signal waveform distortion and therefore reduces signal-to-noise ratio degradation along the line, while a small pulse width is advantageous for the initial signal-to-noise ratio which is determined by the back-to-back transmitterreceiver configuration. A duty factor of 0.6 to 1 is suitable for long-distance transmission at 10 Gbit/s for a fiber dispersion of 0.1 ps/km/nm.