Insulin-incorporated nanoparticles were prepared by polyelectrolyte complex formation using low-molecular weight water soluble chitosan (LMWSC). Insulin-incorporated nanoparticles showed spherical shapes with a particle size of approximately 200 nm. The average particle size, drug content and loading efficiency increased with increasing insulin feed. The zeta potential decreased with increasing insulin feed, indicating that the electrostatic interaction increased with increasing insulin feed. At $^1H$ nuclear magnetic resonance (NMR) spectra, insulin and LMWSC had intrinsic peaks while the peaks of the nanoparticles were similar to LMWSC itself at $D_2O$. However, the specific peaks for insulin appeared as a result of the breakdown of nanoparticles using DCl. When polyelectrolyte complex had dissociated, fluorescein isothiocyanate (FITC)-labeled insulin in the nanoparticles showed similar UV absorption peaks to FITC-labeled insulin only. At the release study, insulin was released continuously from the nanoparticles over 120 h at all formulations. Higher insulin contents induced a decrease in the rate of insulin released from nanoparticles. Consequently, LMWSC and insulin successively formed polyelectrolyte complexes as a nanocarriers and LMWSC can be considered a good candidate for insulin delivery.