The systematically mineralogical study of a swelling chlorite found from Wuding, Yunnan, is reported. The data of form, physical property, chemical analysis, X-ray powder diffraction, thermal analysis, infrared spectrum, electron microscope and changes of the mineral after heating are described in this paper. The untreated chlorite has a 14.68A of d(001)which changs to 16.13A when treating with ethylene glycol and to 14.30A after heating to 550℃(2hrs). Heated above 900t it has been changed into bronzite-hypersthene. The chemi- cal analyses gave, SiO2 34.71,A1203 12.10,Fe203 4.59,Fe0 7.48, Ca0 0.61, Mg0 23.60, H20+10.34 and H20-5.35%·The swelling chlorite is fibrous. In this paper data of X-ray diffraction as well as infrared spectrum patterns while heated to 330 ℃，550℃.620℃ 820℃. 900℃，1000℃ and 1100℃are recorded.