Shear and elongation rheology have been used in order to quantify the interfacial tension properties of PLA_PBAT blends. A multi-functional epoxide (Joncryl) has been chosen as a compatibilizer. From small amplitude oscillatory shear (SAOS), the results show that the addition of the Joncryl into the blends increased largely the shear rheological properties (elasticity, shear-thinning behavior) and contributed to very long relaxation process. This relaxation process is characterized by the presence of a G' shoulder at lower angular frequencies. Scanning and transmission electron microscopy (SEM and TEM) observations show a finer morphology thus confirming the improvement of interfacial properties of the compatibilized blends. The interfacial tension has been firstly quantified using the deformed drop retraction method (DDRM). These experiments elucidated some of the effects of phase elasticity on both deformation mechanism and break-up conditions. A decrease of the interfacial tension has been demonstrated for the compatibilized blends. Secondly, the same trend was also highlighted using the emulsion Palierne model (simplified and generalized versions). Finally, the interfacial tension value was extracted from the measurements of extensional properties. A good accuracy with the two latter methods was obtained. This decrease of the interfacial tension nicely demonstrated the role of Joncryl as an efficient compatibilizer for a better handling of blow PLA-PBAT film extrusion process.