New poly(ethylene-co-isosorbide terephthalate) (PEIT) grades incorporating the 100% biobased isosorbide comonomer clearly opens up new technological perspectives for biobased polymer materials in high-HDT applications. However, the overall biobased content remains low for PEIT polymers (typically less than 15 wt-%) and further improvements of the cost/renewability/properties balance could be performed using poly(L-lactide) (PLLA)/PEIT associations by melt-blending processes to target biobased content higher than 60%. PLA/PET-like blends still remains unexplored and one of the main challenge deals with the optimization of the interfacial compatibility between PLA and PEIT. In this context, we here specifically addressed the effect of the isosorbide comonomer on the PLLA/PEIT interfacial tension in the melt state with subsequent morphologies and mechanical properties. Different industrial grades of PEIxT were selected with various levels of isosorbide content (x from 3 to 14wt-%). The work first focused on the analysis of interfacial properties for the PLA/PEIxT blends in the melt state. At high temperatures, the interfacial tension (determined from rheological analysis and microscopic analysis) decreased with increasing isosorbide content. The improved compatibility in the melt state for PLA/PEI14T blend was confirmed by (i) the refined morphology with the lowest PEIT droplet diameter in PLLA and (ii) the closest surface tensions in the melt state between PLLA and PEI14T evaluated by pendant drop experiments. However, inverse trends are observed on mechanical properties with the best ductility and impact properties observed at low isosorbide contents, i.e. PLA/PEI3T blends. Different mechanisms are postulated and discussed to explain actual trends in PLA/PEIT blends for further blend optimization.