We have measured impurity levels of radioactive isotopes, especially 137Cs and 134CS, in various cesium compounds using HPGe detectors for the first time. The 137Cs contamination levels of cesium iodide (CsI) powder samples that are commercially available were between 9.7 mBq/kg and 80 mBq/kg. With these levels of the contamination, 137Cs will be the most serious background source in the low energy region E < 100 keV for CsI crystal. An upper limit of the 137Cs contamination level in pollucite powder, from which CsI powders are extracted, was set to be 5.8 mBq/kg at a 90 % confidence level. It should be possible to fabricate the CsI crystal with much less 137Cs contamination than the currently available CsI crystal.