The emission cross section of Nd:LuAG was evaluated using two different methods: the Füchtbauer-Ladenburg equation and the threshold-slope measurements; similar results were obtained with both methods. All measurements and calculations were compared with those of Nd:YAG to reduce uncertainty. Detailed spectroscopic properties of Nd:LuAG were demonstrated. The results showed that the peak emission cross section of Nd:LuAG is approximately 20 × 10-20 cm2, approximately 2/3 the emission cross section of Nd:YAG, instead of the previously reported 9.67 × 10-20 cm2. Additionally, the corresponding saturation flux is 0.9 J/cm2. Therefore, the energy storage capacity of Nd:LuAG is not significantly improved, and it is not sufficient for large-scale amplifiers.