Photodynamic therapy (PDT) has already shown immense potential in antitumor fields due to its low systemic toxicity and negligible drug resistance. However, the clinical application of current photosensitizers is still restricted by the low singlet oxygen yield or insolubility. Herein, series of star-like hydroxyl-rich polycations (Pc-PGEA/Pc) with flanking phthalocyanine (Pc) were proposed for effective water-soluble photosensitizers. The designed Pc-PGEA/Pc polymers consist of one Pc core and four ethanolamine and Pc-difunctionalized poly(glycidyl methacrylate) arms. The strong π-π stacking and hydrophobicity of introduced Pc units drive the amphipathic Pc-PGEA/Pc polymers to self-assemble into well-defined cationic nanoparticles. Such Pc-PGEA/Pc nanoparticles present impressive photodynamic therapy effects under moderate irradiation and remarkable photoacoustic imaging (PAI) ability. These kinds of nanoparticles also exhibit good performance as gene vectors. The PAI ability given by the proper wavelength absorbance of Pc units provides one promising method for PAI-guided combined antitumor therapy. The present work would contribute valuable information for the development of new strategies of visible antitumor therapy.