Biodegradable composites of polylactic acid reinforced with wood fiber are fabricated by using twin screw extruder followed by the injection molding machine.The effects of fiber mass fraction and alkali concentration on mechanical properties of biodegradable composites are investigated.The results show that through carrying out the TG analysis of wood fiber,the most suitable temperature for composite materials processing is about 160℃ is chosen,the mechanical properties of biodegradable composites presented tendency which reduced first,elevated,and again reduced along with fiber mass fraction increased,after the alkali treatment,the mechanical properties of biodegradable composites have the tendency which increased first and then reduced,when the concentration of alkali solution is 8%,both the tensile strength and impact strength are best.The scanning electron microscope and Infrared Spectrum Analysis are also used for examination of the wood fiber and biodegradable composites.