To comply with STEP-NC (ISO 14649), a new paradigm for NC programming, many computer systems involved in NC manufacture are required to reshape in both functionality and structure. This paper reports a feature-based NC programming system for prismatic parts to be machined using STEP-NC machine tools. The proposed system consists of three functional modules, i.e. a feature-based modeler, a process planner and a part program generator. The modeler provides a graphical environment for the part model, which is created by adding manufacturing features on a 2.5 D sweep primitive shape. The process planner determines which operations are to be performed for the features, generates workingsteps and then produces a reasonable workplan. Finally both the geometrical and the process information are passed to the part program generator to form a complete ISO 14649-compliant file. The proposed system is demonstrated through the generation of the STEP-NC part program for an example part, and major issues such as the feature-operation mapping and the workingstep sequencing etc are also addressed in this paper.