The essential work of fracture (EWF) approach is widely used to determine the plane stress fracture toughness of highly ductile polymers and related composites. To shed light on how the toughness is affected by nanofillers EWF-suited model polymers, viz. amorphous copolyester and polypropylene block copolymer were modified by multiwall carbon nanotube (MWCNT), graphene (GR), boehmite alumina (BA) and organoclay (MMT) in 1 wt.%. EWF tests were performed on deeply double edge notched tensile loaded (DEN-T) specimens under quasistatic loading conditions. Data reduction occurred by energy partitioning between yielding and necking/tearing. The EWF prerequisites were not met with MWCNT and GR. BA affected the EWF parameters at least. Results indicated that incorporation of nanofillers usually enhanced the specific essential work of fracture, however, at cost of the specific non-essential work of fracture parameter. This means that the resistance to crack initiation and to crack propagation can hardly be improved at the same time with nanofillers.