Phase equilibrium pressure-temperature (pT) conditions for the xenon (Xe)-tetra-n-butylammonium bromide (TBAB)-water system were characterized by an isochoric method in the pressure range from (0.05 to 0.3) MPa using TBAB solutions with mole fractions ranging from (0.0029 to 0.0137). The phase equilibrium pT conditions in the system appeared at a lower pressure and higher temperature than in the pure Xe hydrate. Furthermore, under atmospheric pressure, the dissociation temperature in the Xe-TBAB-water system shifted to a higher region than in the pure TBAB hydrate. In the experimental TBAB concentration range, the powder X-ray diffraction patterns of the Xe-TBAB water system revealed that the TBAB clathrate hydrate is TBAB.38H(2)O.