Multifunctional phototheranostic nanoparticles assembled from photosensitizer molecules have attracted considerable attention the field of tumor phototherapies. However, most self-assembled photosensitizer nanoparticles only exhibit photothermal therapy (PTT) activity, while their photodynamic therapy (PDT) activity is greatly restricted. Here, we first obtained nanostructured ZnPc assemblies with dual-modal PTT and PDT functions upon exposure to monochromatic 650 nm near-infrared (NIR) irradiation. The as-prepared ZnPc nanoparticles not only showed good stability, excellent biocompatibility, and absorption in the appropriate NIR region, but also exhibited high photothermal conversion efficiency (as high as 31.3%) and remarkable PDT performance. The simple synthesis method and outstanding therapeutic effect from synergistic PTT and PDT make the as-obtained ZnPc nanoparticles an ideal phototheranostic agent for effective and safe cancer treatment in clinical research.