This book is published for the researchers to study the stability constant of metal complexes. The determination of formation constants of complexes of some metal ions with ligands have been carried out using Irving Rossotti method in aquesous media at 30 + 0.2o C. Various factors influencing the formation and stabilities of metal complexes are discussed. The overview of coumarin , its derivatives and its metal complexes is given for brief introduction of the work. Different methods are also discussed for the determination of stability constant of metal complexes. The result of pHmetric titration and graphs are given for each metals.