New kinds of narrowly distributed protein-based nanoparticles, bovine serum albumin-Poly (acrylic acid) (BSA/PAA) nanospheres, and nanocapsules were prepared via in situ polymerization, swelling, and re-aggregation. The structure and morphology of the nanospheres were characterized by UV-Vis, FT-IR, DLS, and TEM. The stability of the BSA/PAA nanospheres and nanocapsules was increased when their skeletons were fixed by cross-linked agents. The nanospheres carried a positive charge and their size was about 80–110 nm. The protein-based nanocapsules were stimuli-responsive with pH value and their hydrodynamic diameter varied from 70 to 230nm with changes of pH. In vitro release experiments of Rhodamine B and Doxorubicin hydrochloride showed that these biopolymer nanoparticles provided a controlled release of the entrapped drugs for 300 hr.