Production of expanded clay pellets is possible by using of different hydromica containing clay of Latvia. The chemical composition and grain size distribution of clays have essential significance. The transition to the one-stage firing is possible by addition of leaning materials to the clay, ie., milled sand. The content of Fe(III) is necessary to increase in the raw materials mix for the producing of expanded clay pellets. The using of iron oxide residues is possible. The obtaining of expanded clay pellets with different properties such as bulk density and coefficient of expanding is possible by adjust of chemical composition and grain size distribution. Such expanded clay pellets are with various application possibilities. The pellets of expanded clay obtained by two-stage technology characterise with highest porosity and highest specific surface area. The producing of such pallets is inconvenient with tendency to adhesion between pellets during firing and such pellets have low mechanical strength. The external layer of pellets is thicker and mechanical strength of granules increase by one-stage firing. Expanded clay produced from quaternary clay of deposit Prometejs characterises with the highest porosity and specific surface area. Such pore structure is concerned with presence of large amount of small pores with diameter smaller to 0.1 μm. Expanded clay pellets produced from Devonian clay of deposit Kuprava by one-stage firing characterise with considerably lower porosity and specific surface area. The expanded clay pellets obtained by one-stage from lean Devonian clay of deposit Tuja and Devonian clay of deposit Planci with addition of 25 % of milled sand in comparison with pellets obtained by two-stage firing, characterise higher porosity but lower specific surface area. The external layer of expanded clay pellets by one-stage fast firing is partially permeable structure and is suitable in the sorption processes and technology of microbiology.