This paper examines the stability of the blades that convert the wind kinetic energy into the mechanical energy among the small wind power-generation systems, and proposes the design improvement for blades with a higher rigidity and a lighter weight than the conventional blades. The composite-specimen tensile test and static-load test are conducted to verify the reliability. To design the lightweight blade with the high stiffness, the displacement and the safety factor of the blade composed of the composite material are calculated from the structural-analysis results, and the optimal dimensional and material designs are performed. The optimal design parameters are selected by the shear-web lamination angle and the lamination thickness. The objective function is selected by the safety factor and the weight. For the optimum material design, the GFRP is converted into the CFRP. In this paper, the structural improvement is performed by optimizing the dimensional and material designs, the blade stiffness and weight are redesigned and compared with those of the designed blades, and the structural stability of the redesigned blades is also examined.