The association constants of Li+, Ca+2and Mg+2ions complexing with 1, 4, 7, 10-tetraoxcyclododecane in DHO were determined by the aid of13C dipole-dipole relaxation time measurements. To obtain the Ka, association constant, the TO1values of the stoichiometric complex solutions and the T10of the free molecules were applied to the equation derived, 1/Ka· Ao+ 2 = 1/P + P, for the 1:1 ratio of the complexing and to the equation 1/2Ka·Ao+ 3/2 = P + 1/2P for the 1:2 ratio of the complexing where P, is molar ratio of the crown complexed ions.