Physicochemical transformations that occur during the low-temperature synthesis of zirconium carbonitride via the reduction of zirconia with magnesium in the presence of sodium carbonate in a nitrogen atmosphere are studied. Both reactions leading to the formation of Zr2CN and side processes occurring in the charge are studied by means of differential scanning calorimetry. Based in the results, it is concluded that zirconium carbonitride can be synthesized in the temperature range of 600–675°C. It is shown that using graphite does not lead to the formation of zirconium carbide or zirconium carbonitride in the investigated range of temperatures, while the use of urea has hardly any effect on the final product.