In this study, we successfully synthesized CaAlSiN₃:Ce³⁺ at 1073 K using the ammonothermal method. The synthesis temperature was 900 K lower than that in the conventional solid-state reaction. The product exhibited a broad emission band that was centered at approximately 550 nm by irradiation of 440 nm blue light. Furthermore, we investigated the effects of the reaction temperature and mineralizers on the products synthesized using the ammonothermal method. The results of X-ray diffraction analysis indicated that the optimal temperature for CaAlSiN₃:Ce³⁺ synthesis was 773 K because the sample treated at this temperature exhibited the highest diffraction intensity and the smallest half-value width. The product prepared using NaNH₂ as a mineralizer exhibited the highest emission intensity. Moreover, the products prepared using the ammonothermal method had a plate-like crystal morphology.