HCl capture experiments with rice straw char were conducted in a fixed-bed reactor at 500-900 degrees C. The capture capacities of rice straw char at different temperatures were determined. A significant amount of HCl was found to be captured by rice straw char at all temperatures, and the amount of captured HCl decreased gradually with increased temperature. Analysis of char samples obtained at different thermal treatment times and under different atmospheres showed the effect of HCl capture on the transformation of alkali and alkaline earth metallic (AAEM) species in char. Both the release and occurrence of AAEM species in char significantly changed with HCl capture, based on which the reaction between HCl and AAEM species was analyzed. Desorption experiments showed the importance of adsorption by char at each temperature. The reaction of HCl with AAEM species in char and the adsorption of HCl by the char matrix were proposed to be the main mechanisms of HCl capture by char, and the former was the dominant pathway.