Interpenetrating polymer network (IPN) coatings synthesized from castor-oil-based polyurethane (PU) with chitosan, nitrocellulose, or elaeostearin were coated on regenerated cellulose (RC) film for curing at 80-100 degrees C for 2-5 min, providing biodegradable, water-resistant cellulose films coded, respectively, as RCCH, RCNC, and RCEs. The coated films were buried in natural soil for decaying and inoculated with a spore suspension of fungi on the agar medium, respectively, to test biodegradability. The viscosity-average molecular weight, M-eta, and the weight of the degraded films decreased sharply with the progress of degradation The degradation half-lifes, t(1/2), of the films in soil at 30 degrees C were found to be 19 days for RC, 25 days for RCNC, 32 days for RCCH, and 45 days for the RCEs Rims. Scanning electron microscopy (SEM) showed that the extent of decay followed in the order RC > RCNC > RCCH > RCEs. SEM, infrared (IR), high-performance liquid chromatography (HPLC) and CO2 evolution results indicated that the microorganisms directly attacked the water-resistant coating layer and then penetrated into the cellulose to speedily metabolize, while accompanying with producing CO2, H2O, glucose cleaved from cellulose, and small molecules decomposed from the coatings.