The release of K during thermal utilization of biomass can cause fouling, slagging, and other technical problems, while released K might be recaptured by biomass char. In this work, cellulose char was used as a raw material to avoid the effects of inorganic elements in biomass char. The capture of gaseous KCl by cellulose char was examined at 900-1000 degrees C in a double-layer fixed-bed reactor. The temporal capture pattern was obtained on the basis of an analysis of char samples after capture for different durations, and the stability and association of captured K were analyzed. Cellulose char showed a remarkable ability to capture gaseous KCl. The increase in the K content captured by the char was rapid at first, decreased with time, and eventually reached 0. With the temperature increasing from 900 to 1000 degrees C, the saturated content of captured K increased from 4.1 to 5.5% and reached saturation more rapidly. The capture abilities of char with different pyrolysis degrees were identical. The K/Cl ratio and scanning electron microscopy and energy-dispersive spectroscopy analysis of the captured char indicated that KCl capture by char occurred primarily through the reaction of the organic structure with KCl to generate char K and through the adsorption of KCl. Under an Ar atmosphere, K captured in char was partially released again to the gas phase but an amount remained stable in the char in the form of char-K. This content was approximately 1.7% and was not related to the pyrolysis temperature. Captured K existed mainly as water-soluble and insoluble K. In the thermal stability experiment, both water-soluble and insoluble K can be partly released to gas but more insoluble K was released than water-soluble K, which meant that the ratio of water-soluble K in char obviously increased.