Hydrate equilibrium conditions for tetra-n-butyl ammonium chloride (TBAC) aqueous solutions were experimentally studied and reported in the concentration range of (5 to 40) mass % and the temperature range of (275.45 to 288.05) K at atmospheric pressure. The phase change temperature of TBAC hydrate increased with the increase of the concentration of TBAC aqueous solution when the concentration of TBAC aqueous solution was less than 35 mass %. The latent heat of TBAC hydrate was about 169.2 kJ.kg(-1).