Abstract: In order to improve the properties of sodium alginate and gelatin respectively, sodium alginate and gelatin were used as raw materials, genipin and CaCl₂ were used as the cross-linkers, and the gelatin/sodium alginate interpenetrating polymeric network films were prepared by step-by-step crosslinking method firstly. Then, the gelatin/sodium alginate interpenetrating polymeric network formation was characterized and analyzed by FTIR, and the formation mechanisms of interpenetrating polymeric network were speculated by FTIR results. Finally, the effects of the additive amount of genipin and the mass ratio of gelatin to genipin on the mechanical properties and crosslinking degree of interpenetrating polymeric network films, and the mass ratio of sodium alginate to gelatin on the mechanical properties, fracture morphologies, thermal stabilities, water absorption and retaining properties of interpenetrating polymeric network films were discussed. The results show that when the mass ratio of gelatin to genipin is 200:1 and the mass ratio of sodium alginate to gelatin is 2:1, the mechanical properties, water absorption and retaining properties and compatibility of interpenetrating polymeric network films reach the best. In addition, the mechanical properties of interpenetrating polymeric network films are also superior to that of pure sodium alginate film and pure gelatin film. The addition of gelatin improves the thermal stabilities of interpenetrating polymeric network films at lower temperature zone, while decreases the thermal stabilities at higher temperature zone. Sodium alginate and gelatin interact each other by intermolecular forces, hydrogen bonding, ionic bond and so on, which improves the initial decomposition temperatures and the maximum-rate thermal decomposition temperatures of the two components. The research solves the problem of the poor mechanical properties of sodium alginate and gelatin, and provides a reference for the application of sodium alginate used in medical fields.