The main aim of this research is to study the in vitro photocytotoxicity and cellular uptake of biodegradable polymeric nanoparticles loaded with photosensitizer mTHPP. As the first part of a continued research on conversion of N-sulfonato-N,O-carboxymethylchitosan (NOCCS) to useful biopolymer-based materials, large numbers of carboxylic functional groups were introduced onto NOCCS by grafting with polymethacrylic acid (PMAA). The free radical graft copolymerization was carried out at 70°C, bis-acrylamide as a cross-linking agent and persulfate as an initiator. These results show that the nanoparticles have high loading capacity and stability. These nanoparticles are suitable as carriers for photodynamic therapy in vivo.