Basic problems on the design of fiberglass reinforced plastic (FRP) ship hull structures are considered. The design procedures of FRP structures are considerably different from the conventional method of metal structures. FRP is a kind of composite materials and is inherently heterogeneous anisotropic, and the FRP structural design is closely connected with the FRP material design (in particular, the lamination design of FRP). Specially, compensation of law rigidities of FRP (one of the main faults of the material) is important in FRP structural design-composite constructions such as stiffened panels or sandwich panels. In this report, rigidities of FRP laminated plates (using glass mat and roving cloth) are considered on the basis of classical theory of anisotropic laminates. Further, the large deflection of FRP laminates subjected to hydrostatic pressure is considered by means of approximate method of orthotropic membranes, when rigidities derived above are used.