In the present work, cast thermoplastic starch films were successfully modified by plasma of 1,3-butadiene to reduce water sensitivity. To overcome the difficulties involved in plasma coating of substrates with high water content, high base pressure was used before the introduction of the working gas and mild deposition parameters were employed. The coatings produced at 6 Pa base pressure were smooth, oxygen free and presented low internal stress. After being coated under these mild conditions, cornstarch films were submitted to wettability measurements and atomic force microscopy (AFM) morphological evaluation. Results showed that the coating process improved significantly the cornstarch films' physical properties; water absorption was reduced up to 80%, while water contact angle increased more than 100%. AFM images indicated that the produced coatings cover homogeneously all the different regions of the cornstarch film. (c) 2006 Elsevier B.V. All rights reserved.