This work is a contribution to the study of the mechanism and of the kinetics of the U$_2$C$_3$ formation by the synthetic reaction. The influences of a mechanical and a thermical pre-treatment of the samples on the reaction kinetics were investigated and discussed taking into account other information from the literature. The relative increasing of the U$_2$C$_3$ nucleation rate due to the pulverization corresponds approximately to the surface enlargement of the pulverized material. The activation energy for the synthetic reaction in powder was found to be 94 +- 7 kcal/mol. The negative influence of nitrogen, oxygen and tungsten on the U$_2$C$_3$ formation was reported. In the decomposition of UC$_2$ to U$_2$C$_3$ and graphite, the influences of the morphology of the graphite precipitate and the fast neutron irradiation on the beginning of the U$_2$C$_3$ formation were also investigated.