Abstract: In order to avoid the low solubility of high molecular weight chitosan in aqueous media and the disadvantages induced by acetic acid that is used usually as a solubilizer，water-soluble chitosan (WSC) was investigated. WSC nanoparticles (WSC NP) with various ratios of WSC/ tripolyphsphoric acid cross-linking agent were prepared based on ionic gelation，and were used to load bovine serum albumin (BSA) for release in vitro. Blank and BSA-loaded WSC nanoparticles were examined with diameter 35～190 nm，zeta potential 35～42 mV and spherical shape. FTIR and XRD confirmed tripolyphsphoric groups of tripolyphsphoric acid linked with amino groups of WSC in the nanoparticles. WSC NP loading studies showed that altering concentration of BSA from 0.05 to 1 mg/mL enhanced loading capacity of BSA but decreased loading efficiency simultaneously. Release studies in vitro suggested that WSC had the properties of controlled-release proteins delivery. These results indicate that WSC nanoparticles are promising carriers system for protein delivery.