Star-shaped poly(L-lactide)-b-poly(ethylene glycol) (SPPLA-b-PEG) block copolymers with porphyrin cores were successfully synthesized from the ring-opening polymerization (ROP) of L-lactide initiated with a porphyrin core, followed by a coupling reaction with a hydrophilic PEG polymer shell. The structure of this novel copolymer was thoroughly studied by nuclear magnetic resonance spectroscopy (NMR), Gel Permeation Chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The SPPLA-b-PEG copolymer exhibits efficient singlet oxygen generation and displays high fluorescence quantum yields. Notably, the self-assembly of the as-prepared porphyrin-cored star-shaped copolymer into micelle-like structures provides the great potential of using this well-defined porphyrin core material for drug delivery systems. Particularly, doxorubicin-loaded SPPLA-b-PEG nanospheres exhibit pH-induced drug release properties.