Low temperature heat capacity of ammonium, rubidium and cesium perbromates has been studied by method of adiabatic calorimetry. Anomaly of the heat capacity of cesium perbromate has been found, which corresponds to a structural phase transition. The separation of heat capacity into components has been carried out by the additive scheme. The torsion oscillation of BrO4− anions in solid perbromates at low temperatures has been found. Ammonium ions retardedly rotate aroundC2 axes in the crystal lattice of NH4BrO4.