The aim of this work was to investigate the effect of autochthonous bioaugmentation (ABA) in phenanthrene-contaminated Patagonian soil microcosms, maintained under arid conditions, on phenanthrene elimination and soil microbial community. The polycyclic aromatic hydrocarbon (PAH)-degrading strain Sphingobium sp. 22B previously isolated from the Patagonian soil and selected by its resistance to drying conditions was used as inoculant. The phenanthrene concentration, dehydrogenase activity and denaturing gradient electrophoresis of 16S rRNA gene were monitored during 230 days. The results showed that when the microcosms were maintained at 20 % of soil water-holding capacity (WHC), the phenanthrene biodegradation was drastically inhibited and changes in the genetic diversity of soil microbial community were not detected, and neither the ABA nor the biostimulation managed to overcome the inhibitory effects. When the moisture was slightly increased, reached 25 % WHC, the ABA showed a significant initial stimulatory effect on phenanthrene biodegradation, demonstrating the potential of ABA in PAH bioremediation process in semiarid Patagonia.