Clay ion exchange capacity is an important value for analysing migration of various unacceptablen (toxic, radioactive) additives on surface and ground waters in normal or catastrophic situations. Sorption of the organic methylene blue dye on the natural Latvian clay samples from different deposits - Tūja, Pavāri, Planči, Skaņkalne (devon), Prometējs, Ugāle, Ceplīši (quaternary) and Strēļi (jurassic). For CEC determination of the samples, methylene blue adsorption measurements were used. The studies have proven that CEC of Latvian natural clays is sufficient for using them in the waste water purification from admixtures of the organic dyes. The study results were added to the Latvian clay ion exchange properties database