The position when certain chemicals infiltrated into FRP by immersion test is clarified. X-ray analytical microscope (XAM) was used to observe infiltration of the chemicals. Using XAM the area targeted can be analyzed and images may be acquired which show elemental distribution in the samples. From the images received by analysis, we quantitatively evaluated infiltration quantity in the chemicals, and investigated the effect of this infiltration quantity on the strength. in addition, the effectiveness of degradation accelerated test is also described in this paper. The chemicals which used is 10wt%(1.0mol/l) sulfuric acid aqueous solution.