An optical transmission system is disclosed, in which the transmission of the optical soliton pulses is controlled by controlling the wavelength dispersion of the optical fiber transmission line for each long section including a plurality of optical amplifier repeaters. In this case,the first sections having an average value of the wavelength dispersion larger than the dispersion value meeting with the soliton condition and the second sections having an average value of the wavelength dispersion smaller than the dispersion value meeting with the soliton condition are alternatively allocated in the optical fiber transmission line, so that the average value of the wavelength dispersion of the entire length of the optical fiber transmission line assumes a positive value.