Abstract: The principle of chemical engineering was applied to drug delivery. Am unsteady-state delivery kinetics model with boundary diffusion layer resistance was established to replace the "Pseudosteady-state Assumption" which deviates from the real delivery process. A novel poly (ethylene-vinyl alcohol)/vitamin B12 slab delivery system was designed and used to verify the model. The results showed that the model was effective in describing and predicting the delivery behaviors for a diffusion-controlled polymer/drug release system.