Abstract: The coordination reaction of 2,3-bcnzo-6-methyl-15-crown-5(BCl-15C5)with alkali metal ions was studied in anhydrous methanol by using homemade titr-ation calorimeter of follow-up adiabatic type.The calculated results show that,except the 1:1 coordination compounds,potassium forms 1:2 coordination compounds,but sodium and rubidium do not,and cesium does not react with the crown at all because of its big radius.When methyl was added to crown ring of benzo-15-crown-5,both the stability and coordination reaction enthalpy of 1:1 coordination compounds decreased.This implies that the effect of space hindrance of methyl is stronger than that of increasing electron density on oxygen atom of crown ring.This resembles the effect of methyl to be added to crown ring of benzo-18-crown-6 on coordination reaction studied by us previously.