This document proposes a method to improve query facet mining by leveraging knowledge bases in addition to search results. Existing methods mine facets from frequent lists in top search results, which has limited coverage. The proposed method first generates facets based on entity properties in knowledge bases like Freebase that correspond to the query, and then expands initial facets mined from search results by finding similar entities in the knowledge base. An evaluation shows this approach significantly improves the coverage of facet items over state-of-the-art algorithms.