We analyzed population structure and genetic diversity in Blanco Orejinegro Creole cattle with 12 microsatellite markers, genotyping 138 individuals belonging to 7 commercial and 3 conservation herds.These markers showed a high level of polymorphism; 171 alleles were identified.The mean number of alleles per locus was 5. 63 (3.82-6.58).The total number of alleles per marker was 14.2 and ranged from 16 (TGLA126) to 22 (TGLA227).The mean expected heterozygosity (0.73) was higher than the observed heterozygosity (0.65), with a significant excess of heterozygosity in almost all populations (F IS = 0.09; P < 0.05).This may be due to crossing between different lines of this breed, affecting the inbreeding levels.Analysis of relationships among populations, assessed by principal component analysis and Nei's genetic distances, indicated a close relationship between some herds.Furthermore, analysis of population structure demonstrated a low probability of admixture with Zebu breeds, as it shows the cluster assignment and the F ST values obtained.We conclude that there is high allelic diversity in this breed, even though a low effective population size has been maintained and the level of inbreeding has not been monitored.Therefore, appropriate conservation ©FUNPEC-RP www.funpecrp.com.