Phytoremediation is a biological soil remediation technique using plants and their associated microorganisms to clean-up contaminated soils and improve soils' quality. We tested whether a co-culture between Miscanthus x giganteus (MxG) and Trifolium repens L. would enhance the soil biological quality. The objective was to determine the influence of MxG in mono- and in co-culture with white clover on the soil microbial activity, biomass and density. MxG was tested in mono- and in co-culture with white clover in a mesocosm over 148 days. The microbial respiration (CO2 production), the microbial biomass and the microbial density of the technosol were measured. Results showed that MxG induced an increase in microbial activity in the technosol compared to the non-planted condition with the co-culture having a greater impact. Regarding the bacterial density, MxG in mono- and in co-culture significantly increased the 16S rDNA gene copy number. The co-culture increased the microbial biomass, the fungal density and stimulated the degrading bacterial population, contrary to the monoculture and the non-planted condition. We can conclude the co-culture between MxG and white clover was more interesting than MxG monoculture in regards to the technosol biological quality and its potential for PAH remediation improvement. NOVELTY STATEMENT Our precedent results have shown the benefits of using Miscanthus x giganteus in association with Trifolium repens L. to improve polycyclic aromatic hydrocarbons dissipation and decrease soil ecotoxicity compared to monocultures. In this study we focused on the plant species' influence on the soil's biological quality to improve MxG biomass productivity in the long term and phytoremediation. Many bioindicators were used such as microbial activity, microbial biomass as well as bacteria, fungi and PAH-degrading bacteria density.We showed it was more beneficial to use co-culture instead of MxG monoculture to improve biological technosol quality and in particular microbial activity and biomass as well as fungi and PAH-degrading bacteria density.