The effect of high pressure on the stability of copper(Ⅱ), cadmium(Ⅱ) and zinc (Ⅱ) complex ions with ethylenediamine, propylenediamine, diethylenetriamine has been investigated polarographically. 0.10M KNO3 solution was used as a supporting electrolyte. The concentration of chelating agents was varied from 0.01M to 1.00M. The dissociation constants of metal complex ions were increased with increasing the pressure from 1 atmosphere to 1,500 atmospheres. The increment of the dissociation constant per unit atmosphere varied from 1.1 × 10^-3 % for Cu(dien)₂^{2+ to 5.0 × 10-3 % for Zn(en)₂2+.}