For measuring fiber content of GMT Sheet, moldings should be divided into specimens. And then by burning this specimen, we can get remaining glass fiber ratio. This remaining glass fiber ratio is regarded as fiber content and this process is called 'burning method'. This method yields high value but it can destroy the molding. So any standard method in fiber content measurements isn't established yet. An experimental method is proposed which can be used to measure the fiber content of compression molded glass mat reinforced thermoplastic sheet by image processing. Therefore to predict the fiber content may be useful for determination of optimum molding conditions, charge pattern etc. so far, the burning method has been used for measuring fiber content of glass fiber-reinforced thermoplastic sheet. Then the burning method is precise but breaks the material sheet. In this study, the soft X-pray photograph intensity of the sheet is measured using the image scanner, and the intensity information is worked out by personal computer. We suggested image processing method which can be used to nondestructively measure GMT-Sheet's fiber content. And fiber content measured by image processing method agree well with the one by the burning method. If GMT-Sheet is thick and fiber content is high, fibers overlapped, then photographing soft x-ray is impossible, so the measurements of exact fiber content is difficult.