— This paper discusses an optimum design approach for robotic hands by considering the characteristics of viscoelasticity of food. “Norimaki-sushi” is taken as an example for food. We first show that the dynamic characteristics of such food can be expressed by utilizing the Maxwell model with two layers. Based on dynamic parameters obtained by experiments, we show the relationship among the total working time, the plastic deformation of food after the grasping motion, the hand stiffness, and the operating velocity of the hand. We newly found an interesting behavior of food that allows to find an optimum set of the design parameters for achieving the minimum plastic deformation of food.