The construction of Technosols is an emergent technology based on the assemblage of technogenic materials for ecological reclamation of polluted land and waste recycling. Although this technology is in expansion, knowledge about the microbial communities in Technosols is limited, despite their central role in ecosystem functioning. In this 2-year study, the diversity and the abundance of total and functional microbial communities were characterized in two types of Technosols constructed to reclaim contaminated sites. The structure of the microbial community was analyzed by automated ribosomal intergenic spacer analysis fingerprinting in both types of Technosols, and the taxonomic diversity was further assessed by 16S rRNA clone library sequencing. Real-time PCR was used to quantify the abundance of the total bacterial and crenarchaeal community and of the functional guilds involved in N-cycling. 16S rRNA sequencing showed that Proteobacteria was the main phylum in the Technosols (50-80 %). The other significant phyla identified were Bacteroidetes, Firmicutes, Choloroflexi, and Actinobacteria. Real-time PCR quantification of the abundance of ammonia oxidizers, nitrate reducing, and denitrifying microbial communities involved in nitrogen cycling revealed that bacterial ammonia oxidizers were more abundant than crenarchaeal ammonia oxidizers. A high spatial variability of the microbial community, which decreased with time, was also observed. At the phyla and class levels, the composition of the microbial community in constructed Technosols was similar to "natural" soils. Both the total bacteria and microbial guilds involved in N-cycling were abundant, but in contrast to most natural soils, bacteria and not crenarchaea were the numerically dominant ammonia oxidizers in both types of Technosols. The decrease with time of the variability in microbial community structure support early pedogenic evolution of recently constructed Technosols.