||Poly(lactic acid) (PLA) is the most used biodegradable polymer derived from renewable resources. However, PLA is a brittle plastic with low resistance to fracture. In this study, we tried to increase flexibility and hydrophobicity by melt-blending it with octadecenylsuccinic anhydride (ODSA) which was synthesized by reaction of octadecene and maleic anhydride. After mixing, thermal and mechanical properties of the PLA/ODSA blends (100/5, 100/10, 100/15) were measured. The results showed that at low contents of ODSA, the PLA was miscible with ODSA, and the PLA/ODSA blends had higher hydrophobicity than the neat PLA. The water contact angle of the PLA/ODSA (100/15) reached a value of 95.9°. Moreover, The addition of ODSA decreased the glass transition temperature and crystallization temperature, producing most α′ crystals during crystallization and therefore resulting in the observed exotherm in DSC curves owing to the α′-to-α crystal transformation. Most importantly, the flexibility was improved as the elongation at break increased from 3.1% for the PLA to 15.1% for the PLA/ODSA blend (100/10), in which stress-whitening was observed during tensile testing. The biodegradability of the PLA/ODSA blends was tested using proteinase K, and the results showed the addition of ODSA did not affect the enzymatic degradability of the PLA.