Abstract: This paper describes the determination on the activity of carbonic anhydrase (CA,EC4.2.1.1) of plant species in karst areas of Southwest China. CA was extracted from leaves of Vitex negundo. The thermostability of CA and the effects of anions and metallic ions on CA activity were investigated. CA activity was stable at different temperatures and relatively stable when the concentration of Ca2+ and Mg2+ was lower than 10 mmol.L-1; Co2+ and Cu2+ lower than 0.001 mmol.L-1; and Zn2+, Mn2+, NO3-, Cl-, Br-, I- and NO2 - lower than 0.01 mmol.L-1. CA could be activated by Ca2+ and Mg2+ at 0.001~0.01 mmol.L-1. Thus, CA had a relative adaptability and could maintain the activity well in the ions condition of soilwater and karstwater.