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The effects of copper (Cu2+) on photochemical efficiency, cellular viability and total phenolic content in Prosopis glandulosa leaves were evaluated after 4, 8 or 12h exposure to 0.1, 10 or 100mM Cu2+ using the tissue tolerance test. The results showed that significant reductions (p<0.003) of photochemical efficiency in P. glandulosa leaves were found after 8 h exposure to 100mM Cu2+ compared with controls leaves. The results also showed a significant increase (p<0.05) on electrolyte leakage values in P. glandulosa leaves after 4h exposure to 100mM Cu2+ compared with control leaves. Total phenolic content in P. glandulosa leaves only differed significantly when exposed 12h to the highest concentration of Cu2+. These results suggest that Cu2+ can produce reactive oxygen species that may form hydroxyl radicals that damage proteins and lipids, which in turn causes loss of integrity and reduce photochemical efficiency of leaves. In conclusion, the photochemical efficiency and cellular viability analyses can be used as useful physiological tools to assess early changes in photosynthetic performance of P. glandulosa in response to copper pollution.