Aqueous solutions of various surfactants, such as, sodium lauryl sulphate, lauryl alcohol-7-ethoxylate, cetyl pyridinium chloride, cetyl trimethylammonium bromide, etc., at concentrations above their critical micelle concentration values, known as micellar solutions, and microemulsion solutions consisting of these surfactants and a co-surfactant,n-butanol, have been used successfully to separate mixtures of isomeric/non-isomeric close boiling substances likeo-nitrochlorobenzene/p-nitrochlorobenzene,o-nitrotochlorbenzene,p-nitrotoluene, 2,6-xylenol/p-cresol, -2,4-dichloro-phenol/2,4,6-trichlorophenol,o-isopropylphenol/p-isopropylphenol, from their solid mixtures. Exceptionally high values for the separation factor have been realized and these novel methods appear to be promising for industrial utilization.