This paper reports the influence of anion nature, applied pressure and pH on the retention of copper and cadmium salts by nanofiltration. The retention of cations is shown to depend strongly on hydration energy and charge valency of the permeating co-ion. At more than 5 bars, the ion retention is independent of the applied pressure. At pH < 3, copper and cadmium retention increases, while co-ion retention decreases. Calculations of salt retentions were performed using the Kedem-Spiegler equation. At constant pH and constant concentration, experimental and predicted results were in good agreement.