A soil fulvic acid bas been characterized and the complexation stability constants with cadmium have been evaluated. The average gram formula weight of the fulvic acid is 2775. Three complexes of stoichiometry CdFA, Cd2FA, and Cd3FA have been observed. The respective conditional stability constants at pH 5.7 are 105.3, 109.8, and 1014.0; at pH 6.7 they are 105.6, 1010.6, and 1015.5; and at pH 7.7 they are 106.0, 1010.7, and 1015.4.