Intracellular delivery of therapeutic proteins remains a challenge for the success of protein-mediated disease treatment. We herein develop a robust nanoplatform made with a TME-pH responsive Meo-PEG-b-PPMEMA polymer and a cationic lipid-like compound G0-C14 for in vivo delivery of cytotoxic saporin and breast cancer therapy. This nanoplatform could respond to a TME pH to rapidly release saporin/G0-C14 complexes, which could significantly improve the uptake of cytosolic saporin by tumor cells and subsequent endosomal escape, thereby leading to an effective inhibition of tumor growth.