Purpose: The effect of water sorption on the flexural strength at the proportional limit (FSp) of a denture base mat erial relined with four different denture reline materials was studied. Materials and Methods: Denture base specimens were relined either after 24 hours or 30 days of water immersion. The relined specimens were tested after another period of 24 hours or 30 days of water immersion. Results: Relined denture specimens generally exhibited lower FSp with an increase4 in water immersion time and an increase in the thickness of the reline material. Conclusions: The plasticizing effect of absorbed water molecules explains the general decrease in FSp of immersed relined specimens. The absence of a significant effect that water immersion had on some relined specimens under certain immersion conditions was explained by water sorption into the denture base achieving an equilibrium after a period of water immersion, and the resistance of some reline materials to the effect of water immersion.