Purpose To evaluate the tumor tropism of cytokine-induced killer ( CIK) cells, the movement track in nude mice bearing breast carcinoma and the influence on major organs of nude mice. Methods Separated and prepared CIK cells using human peripheral blood. The transwell migration assay was used to study the migratory response of CIK cells to human MDA-MB-435 breast carcinoma cells. A nude mouse xenograft model ( BALB/c) was established by injection of human MDA-MB-435 breast carcinoma cells. CIK cells labelled with DiI were injected into caudal vein of the nude mice bearing transplantation tumor. Movement track of CIK cells in vi-vo and influence on major organs were observed by living imaging technology, histopathology and immunohistopathology. Results When cultured in vitro during 14 ~20 days, CIK cells reached the peak level in proliferating stage with the maximum proportion of CD3 +CD56 + T cells. Transwell migration assay showed that the migrating number of CIK cells was increasing along with the increasing concentration of tumor cell cultural supernatants. Living imaging technology showed that the fluorescence signal began to appear 24 hours after injection of CIK cells and was strongest at 48 hours. Immunohistochemical technique and hematoxylin-eosin stain showed CIK cells tended to gather around tumor tissue 6 hours after injection, the most at 48 hours, and with some of the remaining cells on 14 day. In the meantime, no pathological damage caused by CIK cells was observed. Conclusion CIK cells have good tropism to the tumor tissue and safety to the normal tissue, and could be used as a promising cell vector for targeted therapy of cancer.