AIM: To investigate the morphological characterization of tumor infiltrating dendritic cells (TIDCs) and tumor infiltrating lymphocytes (TILs) in human rectal cancer. METHODS: Light and electron microscopy as well as im-munohistochemistry were used to observe the distributive and morphological changes of TIDCs and TILs. RESULTS: TIDCs were mainly located in tumor-surrounding tissue. The number of TIDCs in the earlier stage was higher than that in the later stage (P<0.01). TILs were mainly seen in adjacent tissue of cancers and tumor-surrounding tissue. There were more TILs in the earlier stage than that in the later stage (P<0.01). Under electron microscope, TIDCs were irregular in shape and exhibited many dendritic protrusions. It isn’t obvious that cancer cells perforated the basement membrane and TILs were arranged along the basement membrane in the earlier stage. In the later stage, it is explicit that cancer cells perforated the basement membrane and surrounded by TILs. There were contacts among TIDCs, TILs and tumor cell. One TIDCs contacted one or several TILs which clustered around TIDCs. Glycogen granules were seen between TIDCs and TILs. CONCLUSION: The number of TIDCs and TILs is related with tumor progression There exist close relationships among TIDCs, TILs and tumor cell. AIM: To investigate the morphological characterization of tumor infiltrating dendritic cells (TIDCs) and tumor infiltrating lymphocytes (TILs) in human rectal cancer. METHODS: Light and electron microscopy as well as im-munohistochemistry were used to observe the distributive and morphological changes of TIDCs TILs were mainly located in tumor-surrounding tissue. The number of TIDCs in the earlier stage was higher than that in the later stage (P <0.01). TILs were mainly seen in adjacent tissues of cancers and tumor-surrounding Tissues. There were more of TILs in the earlier stage than that in the later stage (P <0.01). Under electron microscope, TIDCs were irregular in shape and extracted many dendritic protrusions. It is not obvious that cancer cells perforated the basement membrane and TILs were arranged along the basement membrane in the earlier stage. In the later stage, it is explicit that cancer cells perforated the basement membrane and surrounded by TILs. There were TOCCs contacted one or several TILs which clustered around TIDCs. Glycogen granules were seen between TIDCs and TILs. CONCLUSION: The number of TIDCs and TILs is related with tumor progression There exist close relationships among TIDCs, TILs and tumor cell.