Two kaolins, one residual and one sedimentary, were submitted to calcination up to the maximum temperature of 1000°C. Changes on physical and technological properties relevant for paper filler applications were assessed. After dehydroxylation up to the temperature of the exothermic effect, some properties, such as pH and density did not diminish much. However, heating beyond that effect accentuates clearly particle aggregation, density, abrasivity and brightness.