This　study　presents　an　experimental　investigation　of　a　free　piston　expander-linear　generator　(FPE-LG)　used　for　organic　Rankine　cycle　(ORC)　waste　heat　recovery　system.　A　FPE-LG　test　rig　using　compressed　air　as　working　fluid　is　established.　The　motion　characteristics,　dynamic　characteristics　and　the　indicated　efficiency　of　FPE-LG　are　analyzed.　The　motion　characteristics　and　power　output　performance　for　different　valve　timings　are　studied.　The　degree　of　symmetry　is　defined　to　evaluate　the　asymmetry　motion　characteristics　of　the　free　piston　assembly.　The　coefficient　of　cycle-to-cycle　variation　(COV)　is　presented　to　evaluate　the　cycle-to-cycle　variation　characteristics　of　the　FPE-LG.　Experimental　results　show　that　the　free　piston　assembly　displacement　profile　is　similar　to　a　sinusoidal　wave　and　the　free　piston　assembly　can　operate　at　high　and　relatively　constant　speed　at　the　middle　portion　of　the　stroke.　The　maximum　power　output　of　19　W　can　be　achieved　when　the　intake　pressure　is　2.0　bar　and　the　operation　frequency　is　2.5　Hz.　The　valve　timing　and　intake　pressure　demonstrate　a　significant　influence　on　the　asymmetric　motion　and　the　power　output　performance　of　the　FPE-LG.　The　indicated　efficiency　of　the　FPE　(left　cylinder)　decreases　with　the　increase　in　the　intake　pressure.　The　maximum　indicated　efficiency　reaches　92.8%　when　the　intake　pressure　is　1.4　bar　and　the　operation　frequency　is　2.0　Hz.　The　indicated　efficiency　firstly　increases　and　then　decreases　with　the　increase　in　the　operation　frequency.　The　COV　of　the　FPE-LG　decreases　with　increasing　the　intake　pressure.　The　motion　stability　of　FPE-LG　improves　with　the　increase　in　the　intake　pressure.　Valve　timing　and　valve　train　should　be　optimized　in　the　near　future.