Glass fiber reinforced plastic (FRP) has several advantages such as higher heat-and chemical-resistance, great insulation and easier formability, especially being lighter and stronger than the metals.Although varying forms of glass fibers are produced for commercial reinforcements like rovings, chopped strands, mats and woven fabrics, etc., the knitted fabrics have not been produced in spite of their large deformability.There are some difficulties to knit glass fiber yarns except of the beta-yarn, and no investigation on knit-FRP has yet been reported.Since the knitted glass fabrics are superior to any other types of materials as a reinforcement, the knit-FRP is expected to be one of the most promising industrial materials by virtue of extremely large deformability.In the present paper, effect of yarn direction and glass contents of knit-FRP on tensile properties and applicability of the rule of mixture to the results obtained have been investigated by using the plane-knit composed of various diameters of a single fiber.The strength at break was found to depend on the structure of knitted fabric in FRP, and to increase with the glass content. It is noteworthy that the strength at break takes the maximum value at the wale direction because the knit-FRP has an anisotropic structure. The strength is independent of the other factors, for example number of fabrics, thickness of FRP, etc., but the rule of mixture could be applied. The elongation at break has a constant value at a higher level of ca. 7%.