The reaction kinetics of ZrN and HfN immersed in a quaternary salt of composition of 28.5% LiCl–36.3% KCl–29.4% NaCl–5.8% UCl3 (in weight percent) were assessed. Coupons of ZrN and HfN were exposed to the quaternary salt at 525–900 °C for 4–485 h. The reaction kinetics of the salt-refractory interactions were assessed through physical and microstructural characterization including scanning electron microscopy, X-ray diffraction and mass spectrometry. The results indicated that ZrN and HfN lose weight under all conditions investigated. While multiple mechanisms were evident, it is proposed that dissolution and oxidation were the dominant reactions that influence the weight loss. For the overall reaction, negative apparent activation energy values of −46 and −28 kJ/mol were observed in ZrN and HfN, respectively. These seemingly anomalous activation energies were associated with the simultaneous occurrence of electrochemical dissolution and surface oxide formation.