Pressure filtrations of the slurry resulted from HCl leaching of a clay have been carried out at temperatures between 25 and 60℃ with the pressure varied from 1 to 5 atm. The filtration rates were compared between the clay calcined at 700℃ for one hour before HCl leaching and the clay without the calcination. At the filtration temperature of 25℃, the calcination had little effect on the filtration rate. As the temperature was increased to 60℃, however, the calcination gave a higher filtration rate. When the filtration pressure was increased from 1 to 5 atm, the cake resistance increased from 8.1×10¹⁰ to 9.3×10¹⁰ m/kg with the calcined clay and 1.11×10¹² to 6.37×10¹² m/kg with the uncalcined clay, respectively. Under a filtration pressure of 1 atm., the water content of the cake was 1.24 g water/g dry cake with the calcined clay and 1.12g water/g dry cake with the uncalcined clay. Irrespective of whether the clay was calcined or not, 90 to 93% of the aluminum in the mother liquor trapped in the cake could be removed by washing the cake three times with a equal volume of water.