An application limit of linear notch mechanics in elastic-plastic solids is proposed, based on theoretical and FEM elastic-plastic analyses ; this limit corresponds to the condition of small-scale yielding in linear fracture mechanics. Moreover, tensile tests of notched plates in practical materials, which are advanced thermoplastics and their reinforced materials by means of short carbon fibers, are carried out. Then, the proposed equation for the application limit of LNM in real materials is examined from the experimental fracture data.