Titanium nitride ultrafine powders were synthesized by an active plasma‐metal reaction method. Gas desorption measurements were conducted to estimate the surface chemistry of the powders after exposure to air and storage at room temperature. H2O, H2, CO2, CO, and NH3gases were mainly evolved. These gases were considered to be formed by the surface reaction of adsorbed gases on surface oxide of the powders and decomposition of hydroxide‐like or ammonialike compounds, which might be produced during a slow oxidation treatment and stor