The inappropriate use and disposal of polymeric materials, combined with their resistance to degradation, produces considerable environmental problems, which encourages the pursuit for a balance between the durability for application and degradation after final disposal. An alternative is the use of biodegradable polymers which, for some applications, present a great potential in non-biodegradable polymers replacements. Poly (lactic acid) (PLA) has been widely applied as an environmentally friendly thermoplastic. PLA meets many requirements as a packing thermoplastic, however its crystallization rate PLA is relatively low and its barrier properties are not adequate such as high water vapour transmission rate for food packing application. In an attempt to obtain improved water vapour barrier properties and increase the crystallization rate, immiscible blends with poly (butylene terephthalate) (PBT) were produced in a co-rotating twin-screw extruder. Significantly improved properties can be achieved in immiscible polymer blends with polymer nanoparticles well disperse in a polymer matrix (Nanoblends). Compatibilized blends with 3, 5 and 10 wt% of disperse phase (PBT) in the matrix (PLA) were produced, as well as an uncompatibilized blend with 5wt% PBT. The compatibilizer used in this study was LOTADER AX 8840, with glycidyl methacrylate reactive groups. Preliminary results indicates that PBT increased the crystallization rate of PLA during cooling of the binary blend. Pure PLA did not crystalize at the same cooling rate. For the compatibilized blends, the cold crystallization exothermic peak during the first heating was displaced to lower temperatures, given the same condition, in accordance with the observation of an increase in the crystallization rate.