Background: Protein or peptide drugs are emerging therapeutics for treating human diseases. However, current protein drugs are typically limited to acting on extracellular/cell membrane components associated with the diseases, while intracellular delivery of recombinant proteins replaces or replenishes faulty/missing proteins and remains inadequate. In this study, we developed a convenient and efficient intracellular protein delivery vehicle. Materials and methods: A cationic liposomal polyethylenimine and polyethylene glycol complex (LPPC) was developed to noncovalently capture proteins for protein transfer into cells via endocytosis. β-glucuronidase (βG) was used in vitro and in vivo as a model enzyme to demonstrate the enzymatic activity of the intracellular transport of a protein. Results: The endocytosed protein/LPPC complexes escaped from lysosomes, and the bound protein dissociated from LPPC in the cytosol. The enzymatic activity of βG was well preserved after intracellular delivery in vitro and in vivo. Conclusion: Using LPPC as an intracellular protein transporter for protein therapeutics, we illustrated that LPPC may be an effective and convenient tool for studying diseases and developing therapeutics.