An object-oriented user interface for a Structural Design Sensitivity Analysis and Optimization Workstation (SDSOW) is presented. The menu-driven interactive system features an object-oriented engineering spreadsheet as a mechanism to visualize, manipulate, modify, and search for the data generated during the interactive design process. A UNIX based windowing system and object-oriented programming techniques have been used to implement the user interface. Specialized engineering spreadsheets have been derived from a general spreadsheet to support specific design activities. The system can be easily extended to include new design activities by specializing the general spreadsheet to the new design tasks. Since the user interface runs under X-window system, it can be ported to several hardware platforms with minimum efforts.