A microcosm experiment was carried out to evaluate the impact of bioremediation of marine sediments artifïcially contaminated with phenanthrene (100 ppm) on benthic communities of bacteria and free-living nematodes from Bizerte lagoon (Tunisia). Bioremediation schemes tested included biostimulation and a combination of biostimulation and bioaugmentation by inoculating a strain of the bacterium Bacillus sp., isolated from contaminated marine sediments. Univariate analyses showed significant differences (p<0.05) between controls and contaminated microcosms. Thus, phenanthrene caused a decrease in the biomass of indigenous bacteria in the water column, at the interface and in the sediment, and a highly significant réduction (p<0.001) of free-living nematode densities. Our results also show that bioremediation resulted in a réduction of the phenanthrene toxic effect on the marine microflora and nematofauna.All tests of biostimulation and biostimulation-bioaugmentation combination showed a net increase in the total bac-terial biomass and densities of nematodes compared to contaminated microcosms. This increase was more pronounced in microcosms of biostimulation and biostimulation-bioaugmentation combination with the addition of different nutrients.