Porous ceramic pellets from Latvian clays were investigated for the purification of wastewater. In the research, two Quaternary clays of deposits Laza and Progress were used with different chemical compositions and grain size distributions. Sawdust as combustible additive was used for the enlargement of pellet porosity. Pellets were fired at 700, 800, 900 and 1000°C temperature. Thermal analysis, X-ray phase analysis, nitrogen adsorption method (BET) and mercury porosimetry method were used for the characteristics of raw clay and fired materials. Sorption activity of pellets was determined concerning substances with molecular and ionic bond during 14 days. The type of clay and firing temperature influences the sorption time. Large number of nano-size pores is formed during the sintering process of clays, and the specific surface area of pores determines the sorption activity. Pellets fired at 700-900°C had the best sorption activity concerning iodine. All amount of iodine is adsorbed during 4 days on the Laza clay pellets, but on the Progress clay pellets during 7 days. Sorption activity of substance with ionic bond (ammonia ion) was small and the best sorption ability was shown by the pellets of Laza clay fired at the temperature of 1050°C. In Quaternary lime rich clay pellets as a result of thermal decomposition of carbonates pH of solution increases in water medium and influences the sorption of substances with an ionic bond, but sorption of substances with a molecular bond is not influenced. Sorption of inorganic substances from wastewater is a selective property of porous clay ceramics. To produce ceramic materials for wastewater purification, clays with a high content of small grains (Ø < 0.005 mm) should be used.