the present work had as objective to study the effect of the firing temperature on the microstructure of two typical clays from the campos dos goytacazes region. these clays are used in the fabrication of red ceramics such as bricks and roofing tiles. clay specimens were prepared through 20 mpa uniaxial pressing operation. the specimens were then fired at 950 oc, 1100 oc and 1250 oc. the phase composition of the clays was identified, before and after firing, by x-ray diffraction. the texture and the microstructure of each clay were evaluated by scanning electron microscopy. the results indicate that the clays show important microstructural changes due to the different mineralogical composition and the proper effect of firing temperatures.