This paper deals with the design problem of a man-on-board(MOB) storage and retrieval warehousing system which is suitable for storing items of small size and light weight. It is assumed that the operator carries out a sequence of retrieving(or storing) operations traveling on a specially designed truck. Considering the operating characteristics of the man-on-board system, an optimal design model is developed in which the investment and maintenance costs of the system are minimized over a time horizon satisfying a set of constructional restrictions. The model is formulated as a nonlinear integer program and a search algorithm is proposed to find an optimum solution.