A type of hydrophilic chitosan nanoparticles encapsulated with BSA (BSA-CS NPs) was prepared through ionic cross-linking technique based on CS and sodium tripolyphosphate (TPP) at room temperature. The influence of formulation conditions on the size of the BSA-CS NPs was investigated. Results showed that BSA-CS NPs with diameter of below 100 nm were prepared when the pH value was 5.0, the mass ratio of CS to TPP was 4, the molecular weights of CS was 40 kDa, and the BSA encapsulation efficiency was more than 50%. This system was also applied in the preparation of ch...