Technical Abstract: Zein is a prolamine protein found in corn and a promising industrial bioplastic. However, for zein to reach its full commercial potential, research must find ways to overcome two main problems: its relatively high cost and its poor resistance to water. In this work, we have modified zein with several isocyanates and diisocyanates. The major reaction pathways have been identified with the help of NMR. For all the isocyanates employed, the surface free energy of the modified zein has decreased, indicating decreased hydrophilicity. The moisture uptake also appears to decrease with isocyanate modification. As expected, the reaction with diisocyanate partly increases the molecular weight of zein. DSC data show single glass transition temperatures in all cases. The mechanical properties of modified zein are either similar to unmodified zein or reduced in some cases. An attempt has also been made to carry out isocyanate reactions on the surface of zein films.