Various N-acyl chitosans with propionyl-, hexanoyl-, nonanoyl-, lauroyl-, pentadecanoyl-, and stearoyl-groups were synthesized and self-aggregated N-acyl chitosan nanoparticles (CSNPs) were prepared by sonication. By the modification with N-acyl groups, CSNPs increased their hydrophobic character and changed its structural features to be more suitable as a delivery carrier. The mean diameters of bovine serum albumin (BSA)-loaded N-acyl CSNPs ranged from 138 to 551 nm. Uniform particle size distribution of BSA-loaded N-acyl CSNPs was observed. The protein loading efficiency of N-acyl CSNPs was about 9495% with lower BSA concentration (0.1 mg/mL) and not significantly different with acyl chain length. With higher BSA concentration (1.0 mg/mL), however, the highest protein loading efficiency was observed with lauroyl and pentadecanoyl CSNPs. The results suggest that lauroyl and pentadecanoyl CSs are interesting candidates for protein delivery system. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012