Traditional passive optical network (PON) systems are based on binary non-return-to-zero (NRZ) modulation format, which results in some disadvantages, such as the lowest system spectral efficiency, Raman crosstalk against radio-frequency (RF) video channels and large fiber dispersion penalty. In order to avoid the above problems, applying orthogonal frequency division multiplexing (OFDM) modulation format in PON systems could be a feasible technique. So a 10 Gb/s intensity modulation and direct detection (IM-DD) 16 quadrature amplitude modulation (16QAM) OFDM-PON downstream transmission over 100 km standard single-mode fiber (SSMF) is experimentally demonstrated. The recorded downstream receiving sensitivity is -26 dBm at the bit error rate (BER) level of 1×10-3 using avalanche photodiode (APD) direct detection. The dispersion penalty can be ignored at 1556 nm wavelength when the transmission distance is less than 100 km.