Unsaturated polyester resin for FRP waterproofing membranes have a disadvantage of shrinking in the process from liquid to solid state. It is fundamentally needed to estimate induced contraction stress of the resin for designing a good waterproofing membrane system. A new technique, in which the resin is poured in a floating frame on liquid of large specific gravity and induced contraction stress is measured, was proposed in the paper. The technique was applied for some resin samples and it was made clear that contraction stress mainly developed in a few ten hours and reached to the levels of 0.1-0.4N/mm^2.
