The type of cations present in the adsorbed double layer of any clayey soil can significantly control the soil's compressibility. This technical note examines the influence of exchangeable cations on the compressibility of a marine clay. An experimental investigation of the compressibility properties of marine clays with a series of monovalent, divalent, and trivalent cations revealed large differences in behavior. The exchangeable cations employed in this study were sodium (Na+), potassium (K+), ammonium (NH+4), magnesium (Mg2+), calcium (Ca2+), and aluminum (Al3+) in order of increasing valency. The results indicate that the compressibility properties are significantly affected by the valence and size of the adsorbed cations. An increase in valency leads to a reduction in compression index, and at a constant valency an increase in the hydrated radii of the adsorbed cations resulted in an increase in compressibility. Further, it has been found that preconsolidation pressure increases with valency of the cations.