Heavy metal content was monitored in small mammals inhabiting agricultural fields and forest of Merja Zerga in North Morocco. Rodents (Mus spretus, Mus domesticus, Apodemus sylvaticus, Gerbillus campestris, Rattus rattus and Rattus norvegicus) were used as bioindicators to examine the effects of metal pollution. Five heavy metals: Cu, Cr, Pb, Zn and Fe were quantitatively analyzed by atomic absorption spectroscopy Varian AA 240 with graphite furnace in various organs. The Highest concentrations of these trace elements were detected in the liver, followed by the kidneys and the heart. The highest concentrations of Pb, Cu, Fe and Cr, Zn were found in the liver of Rattus norvegicus and Gerbillus campestris, respectively. Medium and low levels of contamination were detected in Apodemus sylvaticus, Mus spretus and Mus domesticus respectively. The results suggest that the genus Rattus, Gerbillus and Apodemus can be considered as a bio-indicator that accumulate more trace-metals than the genus Mus. We also investigated the species-response models to some heavy metals.