Effective visualization is important for knowledge discovery when analysing expression profile data. However, existing tools for visually integrating expression profile data with KEGG pathway maps lack extensive interactive visualization operations. KeggExp simultaneously presents the pathway map of one pathway, dendrogram and heatmap of the genes in the pathway and scatter map of one gene, and also provides interactive operations for highlighting specific genes on the pathway map, including differentially-expressed genes, co-expressed genes selected from the heatmap and user-input genes. With KeggExp, researchers, including those without programming skills, can take advantage of its interactive operations to determine key genes or pathways when analysing expression profile data.