A series of amphiphilic diblock copolypeptides (ADCs), 5-(4-aminophenyI)-10,15,20-triphenyl-porphyrin (APP) conjugated poly(L-leucine)-block-polylysine (APP-LnKm) with different molar ratios of L-leucine unit and lysine unit were designed and synthesized. The optimized composition of the polypeptide was determined to be APP-L109K186, which has high fluorescence quantum yield and could self-assemble into micelles in an aqueous medium with mean particle size <30 nm. The in vitro study indicates that APP-L109K186 shows no significant dark cytotoxicity when the concentration is below 200 mg L-1 for HepG2 and He La cells. In contrast, the polymer exhibits apparent phototoxicity with low IC50 values toward HepG2 and He La cells, implying that the potential high photodynamic therapy efficacy of the polymer. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 286-292, 2011