The Xinliaodong Cu polymetallic deposit is a newly-discovered copper ore deposit in eastern Guangdong Province. Chlorite is one of the main hydrothermal alteration minerals genetically related to copper mineralization in this ore district. According to the mineral intergrowth association, the chlorites of Xinliaodong Cu polymetallic ore district can be classified into two types: the chlorite which coexists with sulfide and the chlorite which occurs individually. Both chlorites exhibit foliate, fibrous or vermicular aggregation forms. By means of microscopic and electron microprobe analysis, the authors investigated chemical composition and texture of the chlorite and concluded that chlorites in the Xinliaodong Cu polymetallic deposit have the following characteristics: ① with the increasing altitude, the Si and Mg components of the chlorite related to mineralization increase gradually, the Al, Fe and Mn components gradually decrease, but the regularity is not apparent for the chlorite which had nothing to do with mineralization; ② the two types of chlorite are mainly Fe-rich chlorites composed of prochlorite and brunsvigite; ③ they were formed by hydrothermal alteration of pelitic or mafic rocks, and the phenomenon that Fe-Mg substitution dominates the octahedral substitution suggests that their formation had to do with the iron-rich and relatively acid environment; ④ according to the chlorite geothermometer, the two types of chlorites were formed at temperatures of 166.32～245.62℃(averagely 219.15℃)and the chlorite coexistent with sulfide had a relatively higher formation temperatures, but both of them were in the range of low-moderate temperature; ⑤ the main formation mechanisms of the two types of chlorites were dissolution-crystallization and dissolution-migration-crystallization.