The influence of transition metals (TMs) on the hydriding/dedydriding critical point of NaAlH4 has been studied using the chemical potential method. The theoretical results predict that, if the reaction system reaches equilibrium, most of the TM additives significantly increase its hydriding/dedydriding critical point in the sequence Pd>Co>Zr>Ni>Nb>Hf>Ti>Mn>Fe>V>Cu>Cr and therefore have destabilizing effects on NaAlH4 in the same sequence. Experimentally, the isothermal dehydriding kinetics of NaAlH4 is studied only with Fe, Ti, and FeTi additives. The experimental results show that the destabilizing effect of Fe and Ti additives with coarse particles is very low while more effective destabilizing ability is achieved with fine FeTi particles. These experimental results suggest that the predicted destabilizing effect of TM additive is hindered kinetically due to the coarse particles of additives, and therefore experimental verification of the destabilizing effect of TMs should be performed with nanosized particles.