The aim of this study is to assess the marine environment quality in the Big Casablanca area. A number of biochemical markers were measured in the brown mussel, Perna perna, sampled from four sampling sites characterized by a different degree of contamination and human impacts. As biochemical indices; Catalase (CAT), Glutathione S-transferase (GST), Acetylcholinesterase (AChE), as well as Malondialdehyde (MDA) and Metallothioneine (MT) were evaluated in whole soft tissues of mussels collected from the selected sites. The biomarkers showed statistically significant differences at the polluted sites when compared to the control ones. Our data indicated that CAT and GST activity, MDA and MT concentration in whole mussel bodies, are a higher and significant (p < 0.05) in mussels collected at polluted sites when compared to specimen sampled from control ones. In contrary the response of AChE activity was significantly (p<0.05) inhibited in mussels from polluted sites when compared to control values. The multiple biomarker responses obtained for October 2010 and 2011, clearly demonstrate the potential presence of different contaminants in Site1 and Site2 reflecting the intensity of pollution in these areas.