In the present study we evaluated the effects of two copper sulfate (CuSO 4) concentrations (0.4 and 3 mM) in the culture medium on the biofilm production and photosynthetic compounds concentrations in Euglena gracilis. The results showed that the exposure of E. gracilis to both 0.4 and 3 mM Cu 2+ stimulated the ability of this microorganism to increase its biofilm production with a mean ± SD optical density measured at 590 nm (0.38 ± 0.04, and 0.27 ± 0.07, respectively). In contrast when E. gracilis was exposed to 0.4 and 3 mM Cu 2+ respectively, the growth of cells and chlorophyll a and b content showed significant decrease relative to those showed by the control. These results suggest that the biofilm formation could be considered as metal protection mechanisms in E. gracilis. Finally, these results provide useful and important information for researchers in order to increase the eco-toxicological studies about E. gracilis for its employment in bioremediation programs.