Binding human serum albumin (HSA) of three polyoxometalates (POMs) with the Wells-Dawson structure, alpha(2)-[P2W17O61](10-) (abbreviated as (alpha(2)-P2W17) and two of its metal-substituted derivatives, alpha(2)-[NiP2W17O61](8-) and alpha(2)-[CuP2W17O61](8-) (alpha(2)-P2W17Ni and alpha(2)-P2W17Cu, respectively) was studied in an aqueous medium at pH 7.5. Fluorescence quenching, circular dichroism (CD), thermal denaturation, and isothermal titration calorimetry (ITC) were used for this purpose. The results were compared with those obtained previously with the Keggin structure POM, [H2W12O61](6-) (H2WI2), and the wheel-shaped structure, [NaP(5)W(30)O110](14-) (P5W30). All these POMs bind HSA mainly by electrostatic interactions. Comparison of the physical characteristics and HSA interaction parameters for the POMs of the present work and those studied previously showed that the overall charge of the clusters is not the single parameter governing the binding process and its consequences. In contrast, besides the influences of the structure, the dimension and/or weight of the POMs, the results have permitted highlighting of the importance of each POM atomic composition for its binding behavior.