The fate of Cl in rice straw after pyrolysis in 200-1000 degrees C was investigated through heating of tubular furnace, sequential extraction, and determination using pyrohydrolysis combined with ion chromatography for total Cl, ion chromatography for inorganic Cl, and gas chromatography-mass spectrometry for CH3Cl. The rice straw and/or its chars after pyrolysis were characterized with thermogravimetric analysis, scanning electron microscopy, X-ray diffraction, and X-ray fluorescence. The results showed that, from 200 to 400 degrees C, water-soluble Cl in rice straw char decreased from 60.31 to 40.13% and released Cl was dominated by Cl-CH3Cl (Cl as CH3Cl) and Cl-HCl (Cl as HCl), with a release rate from 10.41 to 16.81% and from 28.76 to 35.34%, respectively. At 400 degrees C, 5.84% of Cl in tar (tar-Cl) was found. In the pyrolysis from 400 to 700 degrees C, in chars, water-soluble Cl changed a little and organic-bound Cl increased from 1.25 to 7.50%, released Cl-CH3Cl and Cl-HCl decreased from 13.41 to 2.42% and from 29.19 to 12.84%, respectively, and tar-Cl increased from 9.19 to 18.14%. At 700 degrees C, Cl as KCl (Cl-KCl) started to release. For the pyrolysis from 700 to 1000 degrees C, the release rate decreased from 40.20 to 4.48% for water-soluble Cl and from 7.50 to 0.34% for organic-bound Cl, a small amount of residual Cl was found in chars, released tar-Cl and Cl-KCl increased from 18.74 to 26.01% and from 17.40 to 64.64%, respectively, and Cl-HCl decreased from 12.80 to 2.16%. Cl-CH3Cl disappeared above 800 degrees C. These results may be caused by the following reasons: the evaporation of water and volatile matter, decomposition and carbonization of organic matter, changes of composition in tar and char, and reactions of various Cl forms. During the whole pyrolysis stage at 200-1000 degrees C, released Cl from rice straw can pose a certain environmental risk. To reduce the release of harmful Cl in rice straw, the measures of fully evaporating water before pyrolysis, pyrolysis temperature above 700 degrees C, and passing the exhaust gas into NaOH and acetone solution in turn can be taken.