Poly(lactic) acid (PLA) is a biodegradable polymer that has attracted interest as a potential substitute for some thermoplastic polymers. However, its advanced brittleness at room temperature represents one of the major drawbacks for its general use. In this work, PLA was modified by reactive extrusion (PLAREx) to enhance the rheological behaviour and to limit its degradation. The modified material was melt blended with acrylonitrile–butadiene–styrene (ABS), and the resultant morphology, rheological, thermo‐mechanical and fracture behaviour were analysed. Since PLA does not have reasonable compatibility with ABS, maleic‐anhydride‐grafted ABS (ABS‐g‐Ma) was used as compatibilizer. The morphology of the PLAREx/ABS samples resulted in the formation of small ABS rods in the matrix. The presence of maleic anhydride contributed to reducing the interfacial energy of the blends and to obtaining finer micro‐domains of the ABS‐rich phase in the PLAREx matrix. In the compatibilized blends, the presence of elongated ABS‐rich phases opposed free crack propagation and contributed to the increase in fracture energy in comparison to neat PLA. © 2020 Society of Chemical Industry