A versatile synthesis of pH-responsive poly(styrene-block-acrylic acid) (poly(St-b-AA)) diblock copolymer modified Fe₃O₄ magnetite nanocomposite (poly(St-b-AA)@Fe₃O₄) was performed for pharmaceutical removal application. For this purpose, the diblock copolymer poly(St-b-AA) was synthesized via reversible addition of fragmentation chain transfer (RAFT) polymerization technique. This synthesized copolymer with –COOH groups were adsorbed onto the surface of Fe₃O₄ to produce poly(St-b-AA)@Fe₃O₄ nanocomposite, which was then used as adsorbent to remove penicillin G. The synthesis of polystyrene homopolymer poly(St) (macro-RAFT agent) and poly(St-b-AA) diblock copolymer was confirmed by fourier transform infrared (FTIR) and ¹H nuclear magnetic resonance (¹HNMR). The poly(St-b-AA)@Fe₃O₄ nanocomposite was characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), thermogravimetry analysis (TGA), FTIR and dynamic light scattering (DLS) analysis. After that the poly(St-b-AA)@Fe₃O₄ was applied to remove penicillin G (an antibiotic) from aqueous solution. The findings indicate that the optimal conditions for maximum penicillin G removal were pH 11, initial penicillin concentration 50 mg/L, poly(St-b-AA)@Fe₃O₄ dose 0.5 g/L and contact time 50 min. Under such conditions, the extent of penicillin G removal was 99.99%. Based on the obtained results, it is found that the poly(St-b-AA)@Fe₃O₄ adsorbent can be used as an effective adsorbent for removing penicillin G from aqueous solutions.