During the design process of the walking robot ALDURO virtual prototyping is used to examine the design studies in a computer simulation, where the different parts can be tested under varying conditions. Virtual prototyping requires detailed simulation models of the systems being developed. It is not su±cient to have separate models for the mechanical, hydraulic and electronic subsystems. A single detailed mechatronic design approach that incorporates all the subsystems, and their in°uence on each other, is required. In this paper we describe the realization of a virtual prototype of the ALDURO, which couples the complex multibody system model, the hydraulic system model and the nonlinear controller. For the implementation of this system the multibody program MOBILE and the hydraulic simulation program DSHplus are used. An interface has been developed for the coupling of these two (formerly stand alone) programs.