Tumor phototherapy is of great significance for the expansion and advancement of cancer treatment methods. Herein, two-dimensional boron nanosheets (B NSs) with a thickness of 2.4 nm exhibiting an excellent photothermal conversion performance were developed via a simple liquid phase ultrasonic stripping method. Following the loading of the photosensitizer agent chlorin e6 (Ce6) and subsequent modification with poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), a B@Ce6-PAH-PAA NS nanomedicine exhibiting dual modal imaging-guided cancer photothermal therapy (PTT) and photodynamic therapy (PDT) properties, as well as outstanding stability was developed. The suitable nano-size (120 nm) of B@Ce6-PAH-PAA NSs can allow drugs to target tumor tissue with an enhanced permeability and retention effect (EPR). The cytotoxicity experiments demonstrated that B@Ce6-PAH-PAA NSs exhibited good biocompatibility even at high concentrations. Furthermore, the in vitro and in vivo experiments showed the excellent synergistic therapeutic effect of this nanomedicine for PTT and PDT.