The generation and behaviour of realcolloids and pseudocolloids of the actinides, 238 pu, 241Am and 244Cm, are investigated in four different Gorleben Groundwaters. Colloids are characterized by ultrafiltration at different pore sizes from 1 nm to 450 nm and various analytical instrumentations. Behaviour of pseudocolloids has been analysed by determining their effects on the solubility and the distribution coefficient of actinides between groundwater and geomatrix. Sorption of actinide ions on groundwater-colloids (generation of pseudocolloid) are examined and the migration of actinides as pseudocolloids is discussed.