This study determined the changes in water sorption property of a denture base resin reinforced with five types of fibre. E-glass, polyester, rayon, nylon 6 and nylon 6/6 fibres were cut into 2, 4 or 6 mm lengths, and added into resin at 3 wt-%. Fifteen specimens were prepared for each length of reinforcing fibres, and for control specimens without fibre, using a mould with 10x10x2 mm dimensions. Water sorption test was performed according to ISO Specification 1567:1999 for the immersion periods of 1 day, 1 week and 4 weeks (n=5). Results showed that water sorption profiles of all groups were time dependent, and that different lengths of the same fibre material affected sorption values non-linearly. The use of different fibres in varying lengths also had a significant effect on water sorption capacity of the resin. The highest sorption value was recorded from the specimens reinforced with 4 mm rayon fibres after for 4 week immersion.