A series of chitosans with different molecular weight were first prepamd by chemical degradation．They were then used to synthesize N-suecinyl-chitosans(SUC-CS) labeled with a fluorescein FITC. They were incubated with K562 leukemia cells for affinity test．Fluorescence intensity of cells was determined by flow cytometry to assess the affinity of N-succinyl-chitosans for K562 leukemia cells．The results showed that the affinity of N-succinyl-chitosans for K562 leukemia cells was strong and declined with increasing their molecular weight．providing primary data of SUC-CS as targeting cartier of anti-tumor drugs．