<p>In this work, clay from Lampang province in Northern Thailand passing sieve size of mesh number 200 and number 325 was characterized. Residues from the clay washing were also characterized and compared. Laser diffraction was used to determine the particle size distribution. Chemical oxide percentages of raw materials were obtained by mean of X-ray fluorescence, and thermal analysis was used to determine the dehydroxylation of kaolinite phase. X-ray diffraction was also used to detect other crystalline phases such as quartz. Scanning electron microscopy was used to investigate the morphology of the clay before and after calcination. The results showed that clay sample passing number 200 sieve size (K200) has slightly more mass loss compared to the clay residues, while the sample passing number 325 (K325) sieve size has noticeably higher mass loss. At selected calcination temperature, the median particle size of K325 sample became slightly larger after calcination due to the opened up of layers of kaolinite sheets from dehydroxylation as can be seen in the scanning electron microscopy images.</p>