Thermal decomposition characteristics of thallous perchlorate are investigated in nitrogen and in air using TG and DTA techniques. Isothermal studies at 380°, 400°, 420° and 440° in air and in nitrogen showed that the relative amounts of the decomposition products, namely, thallic oxide and thallous chloride, depend upon both the temperature and the atmosphere around the sample. At low pressures (5×10-1 mm/Hg) there is volatilization of thallous perchlorate even at 200°. © 1975 Wiley Heyden Ltd., Chichester and Akadémiai Kiadó, Budapest.