Solubility of nitrogen in liquid Fe–Cr–Ni–Mo stainless steel was measured by sampling method in the temperature range from 1723 K to 1923 K under a N2 gas of 1 atm. As a result, the solubility increased with increasing Cr, Mo and Mn content, whilst it decreased with increasing Ni content. In addition, the solubility increased with decreasing temperature. Thermodynamic analysis was carried out taking Fe-20 mass% Cr alloy as a solvent referring to the manner proposed by Anson. The first attempt showed that the calculated solubility, applying the reported first-order interaction coefficients of N against Cr, Ni, Mo and Mn, did not agree with the measured values. This inconsistency was found to be attributed to the interaction coefficient of N against Ni (eNiN Fe20Cr). Therefore, reassessment to derive eNiN Fe20Cr available up to 30 mass% Ni has been made with the data obtained by us and Anson. Thereby the corresponding coefficient was derived as 0.0063 with which the solubility could be well predicted.