Careful measurements have been made of the magnetic susceptibility of the rutile and anatase crystalline forms of titanium dioxide. The magnetic susceptibility of a single crystal of high-purity rutile was found to be (0.067??0.0015)??10-6 emu per gram, and was temperature-independent from 55??to 372??K. Difficulty was encountered in obtaining a good value of the magnetic susceptibility of anatase because of impurities. However, a value of 0.02??10-6 emu per gram was obtained as a maximum value for anatase powder. A discussion is given for the different values obtained for anatase and rutile. ?? 1960 The American Physical Society.