CD40, a member of the tumor necrosis factor receptor superfamily, is widely expressed on various cell types. Some studies show that CD40 expression is related to several carcinomas, where its function remains largely unknown. This study investigated the expression of CD40 on colon cancer, and evaluated the effect of recombinant soluble human CD40L (rshCD40L) on colon cell lines. CD40 expression on the primary colon cancer samples was detected by immunohistochemistry. The expression of CD40 on colon cell lines was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and flow cytometry. To examine the effects of rshCD40L, the growth-inhibitory activity of rshCD40L on colon cancer cell was examined by MTT assay and the proportion of apoptotic tumor cells was examined in the TUNEL assay. Results showed that CD40 is expressed in human colon primary tumor. Expression of CD40 was elevated in 3 out of 4 colon cell lines examined by RT-PCR and flow cytometry. CD40 expression could be induced by interferon-gamma (IFN-gamma). CD40 ligand, rshCD40L, significantly inhibited the proliferation of the CD40(+) colon cancer cell lines. The inhibition could also be enhanced by IFN-gamma in HCT116 and SW48 cell lines. In addition, rshCD40L induced apoptosis of the CD40(+) colon cancer cell lines. Theses results suggest that CD40 present in colon cancer, and rshCD40L may be of clinical use to inhibit human colon cancer growth.