Three Elsholtzia splendens populations, one from an uncontaminated site (Hongan) and the other from two Cu mine sites (Tonglvshan and Chimashan), were studied in hydroponic experiments for the photosynthesis and transpiration under Cu treatment. The results showed that, under Cu stresses, the capacity of photosynthesis in the two populations from Cu mine sites was stronger than that in the non-polluted population. Under 100 μmol/L Cu treatment, the net photosynthesis rates of leaves in the populations from Tonglvshan and Chimashan were 13.15 μmol CO₂ m^-2 s^-1and 12.59 μmol CO₂ m^-2 s^-1, respectively, which were around 13 times higher than that in Hongan population (1.07 μmol CO₂ m^-2 s ^{- 1}). Using efficiencies of light in the two Cu mine populations were 0.0221 and 0.0224 μmol CO2 μmol^-1 photon, respectively, which were about 7 times higher than that in Hongan population (0.003 μmol CO₂ μmol^-1 photon). It was found that there was no significant change in apparent quantum efficiency in the two mine populations and a significant reduction in the non-polluted population under different Cu treatment. The chlorophyll (Chl a and Chl b) contents in the non-polluted population decreased significantly with the increase of Cu concentration, while in the two mine populations, the chlorophyll (Chl a and Chl b) contents increased with lower Cu treatment. Transpiration rates in the two mine populations were less influenced by Cu treatment. However, the transpiration rate in Hongan population was significantly decreased by the Cu treatment, which was 62.74%, 50.96% and 42.6% of the control under 5, 20 μmol/L and 100 μmol/L Cu treatments, respectively. Using efficiency of water in two mine populations increased with the increase of Cu concentration. With 100 μmol/L Cu treatment, the using efficiency of water in Tonglvshan and Chimashan populations was 161.83% and 130.41% of the control, respectively. In addition, it was also found that the decrease of dark respiration rate and the increase of stomatic resistance in the two mine populations were smaller than that in the non-polluted population. In conclusion, these eco-physiological characteristics might be important factors that cause the two copper mine populations grow normally in the Cu-contaminated soils, indicating that the two populations have developed into Cu-resistant populations.