We attempted adsorption of Cl- ion in HCl and NaCl solutions with compounds which were prepared by heating yttrium oxynitrate hydrate, Y-2(OH)(6-x)(NO3)(x)center dot H2O up to 600 degrees C. The X-ray powder diffraction patterns of the compounds obtained by heating up to 200 degrees C was the same as that of Y-2(OH)(6-x)(NO3)(x)center dot H2O; however, it changed to YONO3 in the temperature range from 300 to 400 degrees C and finally changed to Y2O3 above 500 degrees C. In 0.1 M NaCl solution the starting compound and its pyrolysis products little incorporated Cl- ion. On the contrary, in 0.1 M HCl solution the uptake of Cl- ion increased with the treatment temperature, and the maximum value was 3.1 mequiv g(-1) for samples heated above 500 degrees C.