Humio acid isolated from weathered coal was transformed into its calcium and barium salts and its methyl and silyl derivatives with the intention to block either the reactive earboxyl groups or the phenolio hydroxyl groups or both in the molecules, The humic acid and these various derivatives were ammoniated with dried ammonia at ambient temperature, and were then characterized and studied by infrared speotro-scopy, nuclear magnetio resonance spectroscopy, chemical reaction of model tom-pounds and elemental analyses. It was found that ammonia resets chiefly with the carboxyl groups and selectively with the ortho phenolic dihydroxyl groups in the humic said molecules. On prolonged heating at above 100℃, cyclic anhydride will be formed in the hnmio acid molecule via the dehydration of adjacent carboxyl groups, while the ammonium carboxylate groups in the ammonium hnmate will be transformed into amide groups and carboxyl groups simultaneously. On the ground of these results, several notions are proposed which may be of practical value for modifying the manufacturing process and improving the quality of hnmic acid fertilizer, ammonium humate.