The humidity conditioning ability of various ceramic powders was evaluated by the B-value method using a newly developed acrylic-resin container. The powders were filled in a container 1cm in thickness and the opening area of the container was evaluated as the exposed surface area of the compacted powders. The area to volume ratios (A/V, m-1) were fixed at 0.25, 0.5, 0.75 and 1.0 for a desiccator with 0.0152m3 volume. The B-values increased with increasing of A/V, but the differences of the B-values among the samples decreased. The B-values of the samples were classified into two groups, i.e. high-B (diatomaceous shale, sepiolite, selectively leached kaolin) and low-B groups (zeolite, charcoal, Ishikawa diatomite). The difference between the samples belonging to each group was difficult to evaluated merely by their B-values, whereas it was easily distinguished by the increase of amount of water vapor adsorption between 60 and 70%RH of in-water vapor adsorption isotherms. This is interpreted by considering the ratio of the amount of water vapor in the desiccator to the absorbable water vapor in the material. If the ratio is low, the humidity in the desiccator changes near the initial humidity range. Therefore, it is difficult that the characterization of humidity conditioning property of high performance humidity controlled material by B-value. In that case, the amount of water vapor adsorption is a good indicator of the humidity conditioning ability of high B-value materials.