Abstract. – We assessed the diversity of terrestrial isopods according to habitat in the wadi Tahaddart catchment area. The most representative habitat types in the area were selected within an altitudinal range from 0 to 119 m. In total twelve different habitats were sampled on May 2008: four with forest vegetations: a native dense oak forest, a degraded oak forest and two reforestations, three with maquis vegetation (natural and degraded), four at meadows and the coastal habitat of the Tahaddart River mouth dominated by halophilous vegetation. During the study, 2466 oniscideans belonging to 18 species and six families were collected. Terrestrial isopod structure differed among the 12 sampling habitats. The identified species belonged to five biogeographical categories, with 75 % of the species having a Mediterranean-Atlantic distribution and 25 %, a South-West European and North-West African distribution. The reforestation of Eucalyptus camaldulensis exhibited the highest values of diversity (H’ = 1. 89; J’ = 0. 91). Among the forests, the native oak forest of Quercus suber exhibited the lowest values of diversity indices. Except of the coastal habitat of the Tahaddart river mouth, which provided a habitat for a special terrestrial isopod assemblage, the studied sites were separated into open and closed areas based on the Euclidean distance. The distribution structure of the collected species was also analyzed according to altitude and plant assemblage.