An experimental system of direct-detection optical orthogonal frequency-division multiplexing (OOFDM) signal transmission over fiber was successfully built. In this experiment, the 2 Gbit/s quadrature phase shift keging (QPSK) optical OFDM signals are generated and transmitted over 200 km in single-mode fiber. After transmission in single-mode fiber over 200 km the power penalty is less than 2 dB at the bit error rate of 10-6. Comparing of waveform, electrical spectrum and constellation before and after transmission over fiber, the experimental results show that the optical OFDM signal can overcome the effect of chromatic dispersion in fiber.