Biodegradable polymers have emerged as highly effective drug delivery vehicles. We combine N-carboxyanhydride and O-carboxyanhydride ring opening polymerisations to synthesise a poly(amino acid)-polyester graft copolymer capable of encapsulating, and subsequently releasing doxorubicin via acid-mediated hydrolysis. Consequently, the nanoparticles detailed are extremely promising vehicles for the controlled delivery of chemotherapeutic agents.