As the interference between mold parts occurs in a small region, it is difficult to find the interference at the design stage. It is usually found at the assembly stage of injection molds, which delays both design and manufacturing lead-times. Commercial CAD systems with interference inspection functions have been used so far. However, they are very expensive for the mold industry, and inadequate for performing collaborative work over the Internet. An interference examination system executable on a lower cost CAD viewer is required before releasing final drawings in the mold industry. In this paper, an interference examination algorithm for the Web-based interference verification system applicable to a single-level assembly is studied for injection mold design processes. To design a collaborative system executable on the Internet, a lightweight CAD file converted from a CAD data is used as a native file of the CAD viewer with interference verification capability. The validity of the developed system is confirmed through case studies.