In this study the reaction sintering route for the formation of Ca-a-sialon with a composition on the line Si3N4/CaO · 3AlN (Ca0.8 Si9.6 Al2.4 O0.8 N15.2, m = 1.6, N = 0.8) has been investigated. This is compared with the hot-pressing of Ca-a-sialon and the reaction sintering of Y- or lanthanide-a-sialons. The reaction follows the same sequence: first, the formation of a Ca-rich a-sialon phase (m = 1.9) which is gradually transformed to a Ca-a-sialon with a lower Ca concentration (m = 1.2). The gehlenite phase (Ca2Al2SiO7, melilite group) is observed as an intermediate product. A potential advantage of Ca-a-sialon over Ln-a-sialon Full-size image is liquid phase formation at a lower temperature, which has a positive influence on the processing temperature. Moreover, Ca is cheaper than the lanthanides. The solubility of Ca in the a-sialon is in agreement with values found in the literature.