The problem of designing a modular manufacturing lines is addressed. The modules are multi-spindle units and each unit executes simultaneously a subset of operations. This paper presents an approach to select the right spindle units and to arrange them into linear workstations. Our objective is to design such lines respecting technological constraints by minimizing the investment cost, which takes into account the ¯xed costs of workstations and spindle units. The set of all available spindle units and their costs is known. An approach based on integer programming (IP) is suggested and two models are developed. Experiments were carried out which highlight the IP models capacities and limits.