Aim. The transferrin cycle gained increased interest in recent years and it holds promise as an attractive system for strategies of drug targeting to tumors. Neoplasic cells exhibit a large demand of iron and therefore express highly transferrin receptors. As a consequence, transferrin conjugates can preferentially interact with cancer cells. This strategy is exploited nowadays for targeting novel anti-cancer drugs. Recent data showed that ruthenium (III) compounds possess antitumor and antimetastatic effects, due to their affinity for crucial biomolecules (like transferrin). Methods. The paper presents the transferrin-binding properties of some novel ruthenium (III) complexes with general formula RuL2(DMSO) mCl3·nH2O ((Ru-nf) L: norfloxacin (nf), m = 1, n = 1; (Ru-cpx) L: ciprofloxacin (cpx), m = 2, n = 2; (Ru-oflo) L: ofloxacin (oflo), m = 1, n = 1; (Ru-levo) L: levofloxacin (Levo), m = 2, n = 8; (Ru-pip) L: pipemidic acid (pip), m = 1, n = 2, DMSO: dimethylsulfoxide). We investigated, in vitro, the interactions of these ligands with human transferrin through spectroscopic techniques, with the ultimate goal of preparing adducts with good selectivity for cancer cells. Results. All studied complexes interact with human serum transferrin; the molar ratio [complex]/[transferrin] strongly influences the binding affinity. Conclusions. The best interaction between the complexes studied and transferrin is achieved for a molar ratio of 8; the best interaction was registered for Ru-pip, followed by Ru-nf.