The horn-fly, Haematobia irritans, is a world-wide hematophagous pest that causes great economic impact in the cattle industry. The genetic variability and population structure of South-American horn-fly populations are being analysed by microsatellites markers and could be informative for acessing patterns of historical colonization of this invasive species. Microsatellites – tandem repeated DNA sequences with motifs no longer than six base pairs – are codominant markers, highly polymorphic and locus-specific, if not considering rare cases of redundancy. Due to these aspects, microsatellites have been increasingly employed for population genetic studies. This study aims to isolate and characterize polymorphic microsatellite loci for H. irritans. Genomic individual DNA extracts were digested with Rsa I and fragments were linked to specific adapters. Fragments containing AC and AG repeats were selected by hybridization to biotinilated oligonucleotides bound to magnetic beads. The selected fragments were amplified using adapter-specific primers and cloned. Preliminary results from the screening of 58 inserts of this microsatellite-enriched library provided the identification of eight microsatellite loci. Primers were designed based on each microsatellite-flanking sequence and the amplification conditions are under optimization. The level of polymorphism of each locus is currently being evaluated in order to provide informative markers to access the genetic variability, population structure and evolutionary history of this important parasitic species. Financial support: CNPq, FAPESP.