Castor oil-based polyurethane/elaeostearin (PU/Es, 70:30) coating was synthesized and characterized by using infrared spectroscopy (IR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The results indicated that the PU/Es cured at 100 degrees C formed interpenetrating polymer networks (IPNs), and the formation of PU networks was faster than the polymerization of Es, which belongs to free-radical reactions. The intensity of hydrogen bonds in the PU/Es IPNs decreased with increasing Es content in the studied range, suggesting that the partial hydrogen bonds in the PU were broken by interpenetration of Es polymer. The regenerated cellulose films coated with PU/Es IPNs were more readily cured than those coated with only Es. Meanwhile, IR and DSC measurements revealed that chemical bonds exist in the interface between the cellulose film and the coating layer in the coated films, resulting in the strong adhesion. The interfacial bonding strength, water resistivity, mechanical properties, and biodegradability of the cellulose films coated with PU/Es were much higher than those of the films coated with PU.