Acrylonitrile butadiene styrene (ABS) is a widely used thermoplastic copolymer due to its desirable properties such as good mechanical performance (toughness, impact resistance, among others), ease of processability, chemical resistance, and low cost. Nevertheless, the major drawback of ABS is its inherent flammable characteristic which could restrict its use in a wide variety of applications where fire retardancy is required. Phosphorus flame retardants (PFRs) have been utilized in the last decade in ABS as a more environmentally friendly option compared with its halogenated counterparts. Nevertheless, one of the main drawbacks of incorporating PFRs into ABS is normally the deterioration of its mechanical performance. The use of an ionomer, as a compatibilizer, is the strategy proposed in the present work to reduce the negative effect of PFRs on ABS mechanical performance. In this study, two different PFR additives, selected regarding to high efficiency of flame retardant effect on ABS, and a commercial ionomer were incorporated into ABS by means of a melt blending process. Hence, the effect of adding a commercial ionomer on the ABS and ABS phosphorus flame retardant (PFR) formulations (ABS-PFR) was analyzed by means of different characterization techniques.