We propose a dispersion-tolerant optical duobinary transmission system which uses a binary intensity modulation direct detection (IM-DD) receiver, The proposed system also relaxes the fiber input power limitation due to stimulated Brillouin scattering (SBS), Tolerance to chromatic dispersion in the proposed system is estimated by a simulation, A 10 Gb/s optical duobinary signal can be transmitted over 200 km of standard single-mode fiber (SMF) with 1 dB dispersion penalty, The advantages of the proposed system are confirmed experimentally, The optical duobinary signal was successfully received by the binary IM-DD receiver at the same sensitivity as a binary IM signal, Power penalty due to chromatic dispersion over a 164-km standard SMF was about 1.8 dB at 10 Gb/s, The SBS threshold of the 10 Gb/s optical duobinary modulated light was more than +20 dBm.