A preliminary experimental investigation of a free piston expander-linear generator (FPE-LG) prototype was presented. The aim of developing this FPE-LG prototype was to applied it in a small scale organic Rankine cycle (ORC) system for vehicle waste heat recovery, which can convert the thermodynamic energy of working fluid into electric energy. Technical feasibility of prototype using a newly developed valve train was verified. The phase matching of different cam plates, free-piston motion characteristics, as well as the power output of FPE-LG was identified based on the compressed air test bench. Experimental results showed that FPE-LG can run stably under the condition of high inlet pressure. The cycle-to-cycle variations of velocity at the reference position and the cycle-to-cycle variations of displacement at top dead center and bottom dead center can be ignored. The peak velocity of free-piston was close to 1.2m/s when the intake pressure was 0.2MPa and working frequency was 2.5Hz. The valve timing and intake pressure had an important influence on the motion characteristics of free-piston and power output of linear generator. Decreasing the exhaust duration angle or increasing the intake duration angle can improve the stability, symmetry of free piston, reduce cycle-to-cycle variation of free-piston motion and improve the power output obviously when other parameters were constant. The maximum peak power output was about 19.0W when inlet pressure was 0.19MPa and working frequency was 2.5Hz.