Mechanical design can be classified into stiffness design and strength design. In the stiffness design, the stiffness or deformation of members is concerned, and the enhancement of dynamic characteristics such as natural frequency or damping capacity of members or systems is also important. While, in the strength design, the primary concern is the enhancement of load carrying ability of members or systems. Fiber reinforced composite materials offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials. Because of their low specific gravities, the strength-weight ratios, and modulus-weight ratios of these composite materials are much superior to those metallic materials. Composite materials can be tailored to meet the specific requirements of each particular design. Available design parameters are the choice of materials (fiber, matrix), the volume fraction of fiber and matrix, fabrication method, number of layers in a given direction, thickness of individual layers, type of layer (unidirectional or fabric), and the layer stacking sequence. The greatest disadvantages of composite materials are the costs of the materials and the lack of well-defined design rules, therefore, composite materials should be applied in the right place with appropriate design rules. Up to now, the fiber reinforced composite structures are mainly employed in the strength design such as aircraft, spacecraft and vehicles. In this paper, the novel application examples of composite structures to components for the robots, machine tools and automobiles are addressed considering the stiffness design issues of composite structures. (C) 2004 Elsevier Ltd. All rights reserved.