Bacterial cellulose (BC) fiber reinforced unsaturated polyester (UPE) composites were fabricated using the resin transfer molding method. The mechanical properties, moisture absorption behavior, and photodegradation of the composites were studied. Scanning electron microscopy observations indicated that BC nanofibers surface-treated with silane exhibited higher fiber-resin adhesion strength in comparison to original BC. It was noted that the process of moisture absorption of the BC/UPE composites could be described by using Fick's law and an oxidative degradation took place when the composite is exposed to ultraviolet radiation. (C) 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 249-256, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20220