Effects of nitric acid treatment on content, cation exchange capacity, optic nature and adsorptive characteristics of extractable humic acid in Shanxi brown coal were studied with the ion-exchange equilibrium method. Results show that content of extractable humic acid increased by 45.8% by treatment with nitric acid of certain concentration, thus consequently bringing up its cation exchange capacity, But the two changes were not conincident, with the latter lagging behind the former. Besides, optic characteristics of the humid acid in the acidtreated brown coal were greatly changed too. Its adsorption capacity of NH₄⁺, and K⁺ was significantly increased by 58.73% and 41.53%, of which the isothermal adsorption equation fitted the Freundlich equation and Langmuir equation, respectively. However, contrarily, the adsorption capacity of P was significantly lowered. Its variation could well be described by the Langmuir equation. The changes in the physic-chemical properties of extractable humic acid in the brown coal make the coal fitter for application as slow-release fertilizer.