Dendrimer-encapsulated Pt nanoparticles can be synthesized by Pt2+ coordination with dendrimers followed by reduction. In the present study, we have systematically investigated the coordination kinetics of PtCl42- with fourth-generation hydroxyl-terminated poly(amidoamine) (PAMAM G4-OH) dendrimers using UV-vis spectroscopy measurements. Our experimental investigation clarifies that Pt2+ coordination with dendrimers occurs after the H2O ligand exchange (aquation) of PtCl42-and that a resultant species PtCl2(H2O)(2) predominantly coordinates with the dendrimers. From these results, we have proposed a simple dynamic model that describes the Pt2+ coordination as a consecutive reaction composed of the aquation reaction of PtCl42- and a subsequent coordination reaction of the resultant PtCl2(H2O)(2) with the dendrimers. Our proposed model is in good agreement with the experimental results at a low concentration condition of PtCl42-, validating its performance. Furthermore, we suggest that the proposed scheme can be generalized and applied to metal species other than Pt2+.