Biodegradable and pH-sensitive graft copolymers based on polysuccinimide (PSI) were synthesized as intracellular drug carriers. Hydrophobic octadecylamine (C-18) and hydrophilic O-(2-aminoethyl) polyethylene glycol (PEG, Mw 5000) were grafted on a PSI backbone for amphiphilicity, enabling the formation of a self-assembled micellar structure in aqueous medium. Biotin was conjugated at the end of the PEG segment as the cell penetrating ligand, and hydrazone hydrate was introduced as a cleavable linkage for the release of pH sensitive drug, doxorubicin. The chemical structure of the polymer and degree of substitution of the graft segments were confirmed by Fourier transform infrared (FTIR) and H-1 NMR spectroscopy. The size and distribution of the polymer micelles were investigated by dynamic light scattering. The average diameter of the polymer micelles was 290310 nm with a narrow distribution. Less than 30% of the total DOX loaded in the polymeric micelles was released at pH 7.4, whereas >75% was released at pH 5 in 70 h because of the cleavage of the hydrazone bond in acidic conditions. For the cytotoxicity test, the MCF-7 cell viability in the presence of biotin-conjugated polymer was much lower than that in the presence of a nonconjugated one, as the former had higher probability of cell penetration aided by a biotin ligand. The DOX uptake in MCF-7 cells was analyzed by the confocal laser scanning microscopy. More DOX uptake was observed in acidic conditions because of the cleavage of hydrazone groups in the polymer.