Seashell has excellentmechanical property, which owes to its crossed lamella structure. Seashell is a type of natural composite material. In the viewpoint of material design, learning from nature is a best choice in nowadays. The fatigue damage accumulation in seashell is assessed in the present paper. As compared to the deformation behavior of simple tensile process for the original seashell specimen, the fatigued seashell specimen exhibits lower elasticity modulus, fracture strength and yielding flat free in its stress Â strain curve; It is found that the relative decrease of the fracture energy density of the fatigued sample with respect to the fresh one coincides with the relative decrease of the elasticity modulus of these samples, it implies that the relative decrease of the fracture energy density could be taken as a proper damage variable to characterize the damage accumulation in the fatigue process of seashell.