We propose a duplex multiple-user radio over fiber-passive optical network (ROF-PON) system based on multitone generation and sextupling technique. A dual-drive Mach–Zehnder modulator (DD-MZM) is used to realize the multitone generation. By controlling the modulation voltage of the DD-MZM, the odd carriers can be suppressed which makes the adjacent frequency gap twice the frequency of the local oscillator frequency. Due to the multitone generation and pure carrier reuse technique, the base stations (BSs) are also source-free. The system can support more than one BS simultaneously for a transmission length more than 50 km. The proposed multiuser ROF-PON is scalable and cost-effective, and its feasibility is successfully verified by simulation.