The effect of a prior firing of three montmorillonite clays, exhibiting different nature of interlayer cations, on the rheological behaviour of related aqueous suspensions (5 and 10. mass% of solid content) was examined. Calcinations were performed at 150 °C, 250 °C, 300 °C or 450 °C for 30 min. The rheological properties were characterized at 25 °C in the flow mode using the Herschel-Bulkley model. The alkaline interlayer cation (Na) tended to increase the yield stress of montmorillonite suspensions in comparison with earth-alkaline ones (Ca, Mg). As expected, increasing solid content led to increasing yield stress. For calcinations until 200 °C, the relevant suspensions exhibited an increasing yield stress due to a gel-like behaviour in relation with a card-house-like structure. Furthermore, calcination above 300 °C favoured the decrease of the corresponding yield stress. This behaviour seemed to be related to the modification of the surface properties of the clay platelets, more precisely to the beginning of clay dehydroxylation.