Relative to the extensive study on the relationship between the structure and properties of polyurethane (PU) and polyurethaneurea (PUU), basic information available on hydrated PUU is limited. In this study, PW films were immersed in a saline solution (0.9 wt % NaCl, 37 degreesC) for periods of up to 60 days and evaluated by the change in static and dynamic mechanical properties, composition, and hydrogen-bonding structure. It was found that immersion in a saline solution could greatly increase the average molecular weight and degree of phase separation, which enhanced the mechanical strength and reduced the flexibility. The increase in the average molecular weight is believed to come from the chain extensions or crosslink reactions between intramolecules and/or between intermolecules and from the leaching out of poly(tetramethylene oxide) (PTMO) oligomers. FTIR analysis indicated that H2O molecules did not obviously alter the hydrogen-bonding structure of PUU.