By exchange of cations of different humates (synthetic, brown coal and compost humates) with an equivalent amount of long-chain organic cations, derivatives with the following alkylammonium ions were prepared: n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl and n-octadecyl ammonium ions. X-ray diffraction of the humic acids and the alkylammonium humates revealed a behaviour similar to that of smectite-type clay minerals. The results seem to support the layer structure of humic substances. The layers of synthetic, brown coal and compost humate are about 0.60, 0.45 and 0.84 nm thick, and the bilayers of alkylammonium cations are bound to the carboxyl and phenolic hydroxyl groups. The chain tilt is 41–45 .