RE2O2CN2 (RE = La, Eu, and Gd) and Eu-doped RE2O2CN2 (RE = La and Gd) phosphors were prepared by nitridation of oxide precursors through rare earth citrate gel. This preparation method increased the doping limit to 20 atom % in La2O2CN2. The value was considerably wider than 7 atom % of solid-state synthesis through rare earth oxide. Eu-doped Gd2O2CN2 was firstly synthesized by this method. The shape of luminescence spectra and luminescence intensity were different between these oxycyanamides reflecting the difference in their crystal structure and crystallinity.