New alkyl imidazoline derivatives have been synthesized as potential anti-cancer agents. The anti-proliferative activity of these compounds, evaluated against representative human haematological and solid neoplastic cell lines, showed that N, N'-di (4,5-dihydro-1H-imidazol-2-yl)3-aza-1,10-decane-diamine (8) and N, N'-di (4,5-dihydro-1H-imidazol-2-yl)3-aza-1,10-dodecane-diamine (9) were the most active compounds; in fact, they inhibited the cell proliferation at submicromolar concentrations. In enzyme assays, compound 9 turned out to be an inhibitor of topoisomerase II at concentrations comparable with those of the reference topoisomerase II inhibitor, etoposide.