In this work ,we have reported the synthesis and spectroscopic characterization of captopril (Cap)coordination compounds:Cu(Cap)· 2H2O ,Cr(Cap)· H2O ,Zn(Cap)· 3H2O and Mg(Cap)4 .Herein ,it is worthily mentioned that the FTIR spectroscopic technique was employed to recognized the nature of coordina-tion between captopril ligand and copper ,chromium ,zinc and magnesium(Ⅱ) metal ions .In view of the infra-red spectroscopic tool ,the copper(Ⅱ) metal ion coordinated toward captopril drug ligand through sulfur atom of SH group dependent on the absent of stretching vibration band of —SH .Based on this result ,the stretching motion of νa (COO) shifts clearly indicates that Cu2+,Cr2+,Zn2+ and Mg2+ the carboxylic group is employed as coordinative site for all compounds as a metal-ligand coordinative bond .As a general behavior ,it is verified that the coordination compound thermal stability (considering the release of captopril molecules ,not the re-lease of water molecules) is affected by the metal cation radius:minor radius is associated with higher thermal stability ,probably due to a higher metal-captopril bond dissociation enthalpy .