Chloritization is an important alteration type of the metallogenic stage in the Dafushang uranium deposit. Two kinds of generation form of chlorite were revealed by microscopic characteristics, i.e., the amoeboid aggregate growing along the crack of feldspar or quartz and the alteration of biotite. The results of electron microprobe analyses show that the chlorites from the Dafushang uranium deposit are iron-rich prochlorite, the temperature range of formation of chlorite is 201.48~224.20℃ (averagely 213.65℃), belonging to the mesothermal-epithermal alteration, and the formation mechanism is composed of dissolution-crystallization and dissolution-migration-crystallization. The composition characteristics of chlorite have important significance for investigating the environment of uranium metallogenesis and evaluation of deposits.