By use of optical microscopy (OM), Micro-energy disperses X-ray fluorescence (EDXRF) and X-ray diffraction (XRD), ceramic samples from the Thnal Mrech kiln (TMK) and the Bang Kong (BK) kiln were analyzed systematically to determine the ancient Khmer porcelain production process and its features. The analysis indicated that different types of porcelain clays were used at the two kilns. The body material of the celadon from TMK has high content of SiO2 and lower content of Al2O3, and the clay was extensively treated before use. The difference in color between the porcelain body and the glaze may relate to content of Fe2O3 and TiO2. Grass and wood ashes were found to have been used as a flux in both kilns. In term of chemical composition of the glaze, celadon of the two kilns belong to calcium glaze type. However, some of black glaze from BK is of the calcium-alkali type and some is alkali-calcium. Moreover, the firing temperature of the two kilns was higher than 1200[degree]C, but neither kiln had strict criterion with regard to regulation of the firing temperature. These analytical results have important relevance to research on the history of Cambodia ceramics and the cultural exchanges between China and Cambodia.