Poly(amidoamine) dendrimers (PAMAM) are polymeric macromolecules that can find their use as carriers of oncologic drugs, including among others fludarabine monophosphate. Fludarabine is a potent drug used in a chemotherapy to treat leukemia and lymphoma. However, its use is limited, because of its relatively high toxicity. The architecture of PAMAM dendrimer belonging to the fourth (G4) generation create a semi open-type structure, which facilitate small ligand molecules to bind with them. Hydroxyl terminated PAMAM dendrimers are better tolerated by organism compared with their cationic (amine-terminated) equivalents. The aim of our study was to evaluate the number of molecules of fludarabine monophosphate combined by a macromolecule of PAMAM G4, and the equilibrium constant of the drug combined to the dendrimer functional groups in aqueous solutions. The formation equilibrium of PAMAM G4 dendrimer complex with fludarabine in aqueous solution at room temperature was examined. Using the results of the isothermal titration calorimetry and equilibrium dialysis, the binding parameters such as: number of drug molecules bound to the dendrimer molecule, enthalpy, entropy and the equilibrium constant of the formed dendrimer-drug complex were evaluated. These parameters confirm the strong interactions between fludarabine monophosphate and PAMAM G-4 dendrimers. Acknowledgments: The study was financed from the Grant for Development of Young Researchers from the Faculty of Chemistry, University of Lodz, 2017.