The crystallinity of PLA which was blended with POE and POE-g-MAH together with main mechanical properties were studied. Contact angles increase in the following sequence: PLA, POE-g-MAH, POE. The crystallinity of PLA which were blended with 5 wt% POE is higher than untreated PLA while POE-g-MAH bring down the crystallinity of PLA. For POE, The 15 wt% portion in the blend with PLA is enough to make optimal toughness. Tensile strength of the blends is not decline but increase a little when POE is used in small amount (less then 5wt%) on account of the high crystallinity. All of those lead to a result that not only the tougher, but also the crystallinity of PLA itself play important role in mechanical properties of the blends.