The applicability of the essential work of fracture (EWF) in SENB geometry as an alternative to the J-integral methodology has been assessed. An amorphous poly(lactic acid) (PLA) with ductile behaviour promoted by a de-ageing heat treatment has been used. The results demonstrate that the EWF technique can be used as a simple alternative methodology to determine the J0.2 value in plane strain conditions, using the ESIS-2000 protocol and ASTME813-87 standard. As a validation of the range of ligament length to be used in the EWF analysis, the SENB solution of the Slip Line Field theory could be employed.