The absorption of water by denture base materials is important because it is directly related with dimensional stability of dental material. In this study, water absorption of denture base materials reinforced with different type of dental fiber systems was compared. The samples were prepared from heat-polymerized and microwave polymerized denture base resins and reinforced with different dental fiber systems. Five different reinforcement materials were used in this study, namely, (1) no fiber (control group), (2) plasma-treated crosslinked polyethylene fibers, (3) plasma-treated woven polyethylene fibers (4) porous polymer preimpregnated continuous unidirectional glass fibers, and (5) woven glass fibers. The water absorption calculations were done for the periods of 7, 14, 21, and 30 days of water immersion and in total 100 specimens were tested. The statistical analysis via analysis of variance and Duncan multiple comparison tests have shown that the fiber reinforcement significantly influence the water absorption. Moreover, the results have shown that water absorption of denture base polymers is higher when the specimens are reinforced with the fiber systems. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1750-1753, 2010