This study reports the stability constants of complexes with vitamin D 3 and Al 3+ , Cd 2+ , Gd 3+ and Pb 2+ ions in a water-ethanol medium (30/70% v/v at 25.0 • C). The logarithms of the overall stability constants are: β 1 = 12.4 ± 0.5, 7.6 ± 0.3, 9.33 ± 0.07, and 9.1 ± 0.5, respectively, whereas the logarithms of β 2 are 24.4 ± 0.5 (Al 3+), 14.3 ± 0.3 (Cd 2+), and 15.4 ± 0.5 (Pb 2+). Gd 3+ forms only the 1:1 complex. These values are compared to those reported previously and correlations are established between the stability constants and physical properties, such as the ionization energy.