Abstract Considering the increasing interest for protein immobilization on nanoparticles, in this work, we demonstrate the preparation of poly(styrene-co-maleic anhydride) (PSMA) nanoparticles and their capability to conjugate the proteolytic enzyme papain. PSMA nanoparticles were fabricated by combining precipitation and electrospray technique. Different experimental conditions were tested in order to optimize nanoparticle dimensions and production yield and different techniques were used to characterize the produced nanoparticles. Their mean diameter was found to be 176 nm. The successful papain-nanoparticle conjugation was then demonstrated. The residual catalytic activity of the conjugated enzyme was studied and found to be around 79% respect to the free enzyme.