Abstract: Uncatalyzed blends of bisphenol A dicyanate ester/epoxy novolac with different molar ratios were prepared. Hydrothermal ageing for times up to one month was performed and water take-up profiles of those blends were determined by a gravimetric method. It was found that the blends absorbed much less water than homopolycyanate when the molar fractions of the cyanate group in the blends were greater than 0.5. Dynamic mechanical analysis and FTIR determination were performed on virgin and aged samples. The results demonstrate that the hydrothermal ageing resistance of the blends is superior to that of homopolycyanate.