The fracture behaviour of PLA/PA bioblends has been investigated in order to extend its processing through fused deposition modeling printing by pellets supply (FDM-p). The viability of the processing technique in creating in situ microfibrillated composites (MFCs) through the microfibrillation of the PA dispersed phase has been evaluated as a way to strengthen and toughen PLA. The mechanical behaviour was assessed through uniaxial tensile tests performed at room temperature (22oC) using type 1BA dumbbell tensile test specimens (ISO527-2) featuring an unidirectional infill pattern fully oriented in the longitudinal direction of the samples. The fracture behaviour was assessed through the determination of the CTOD value just before the crack propagation onset in single-edge-notched tension (SENT) test geometry featuring a multi-axial multilayer infill pattern. For all the samples, a nominal filling density of 100 % was predefined. Morphological observations revealed that the 3D printing conditions used in this study allowed the manufacturing of in- situ MFCs with an average diameter of the PA microfibrils as low as 320 nm. The developed morphology led to a significant increase in the structural integrity of the parts manufactured through FDM-p, as clearly evidenced by the 206% increase in the CTOD values as compared to samples obtained through conventional compression-moulding using the same raw pellets.