This paper discusses the development of a design tool which supports a process for constructing PVC-based, ATM networks. Because of mathematical complexities, a heuristic approach has been adopted to find an optimal network configuration. Through a GUI, users define a physical network, and PVC networks which are logically constructed within the physical network. Based on the defined network configurations and user traffic demand, the tool evaluates performance measures. In response to the results of the evaluation, network designers can modify the network configuration to improve the performance. With the aid of this tool, they can repeat this interactive process until the estimated performance measures meet a desired quality. The tool has been applied to the design of several private ATM networks which will be constructed in the near future. The response time of this design tool is so fast that wait time can be negligible.