In this work, the formation conditions of 3.3’-diamincarbanilid (MDAK)- copper(II) complex were studied and stability constant determined spectrophometrically. There was no effect of oxygen on the complex formation. The composition of complex were determined as Cu/MDAK = ½ at pH = 5.66 by Job’s method of continious variation. Also, the pH effect on the complex formation was not seen until pH=5.22. After this point, the reaction rate was increased as a function of [ OH- ]^0.5. It was concluded that the composition of the dark brown coloured complex which was precipitated at pH = 7.30 was [ Cu(MDAK) (OH)₂] and the structure of [ Cu(MDAK) (OH)₂]²⁺ complex which only existed in solution at low pH was changed during the precipitation. The stability constant of the soluble complex was determined as log K = 5.615 by using of the ligand excess method and log K= 5.833 by using the equal absorbed solutions method. Keywords :