In the last century, the wide use of Guzerá breed in crossbreeding led to the expressive reduction of their effective population size, to worrying numbers. Due to its adaptation to diverse environmental conditions, its potential for dual-purpose production (i.e. meat and milk), and its risk of extinction, in 1991, this breed was included by FAO (Food and Agriculture Organization of the United Nations) in the list of genetic resources to be preserved. In view of this, and due to the demand for breeding programs in the country, CBMG (Brazilian Center for the Improvement of Guzerá), at that time the technical division of ACGB (Brazilian Association of Guzerá Breeders) expressed interest in promoting the conservation and breeding of the breed through modern selection and breeding techniques. In 1994, the National Dairy Breeding Program for the Guzerá Cattle was implemented in Brazil, based on the progeny testing and open MOET ((Multiple Ovulation and Embryo Transfer) Nucleus breeding schemes, which evaluated bulls based upon the productive performance of their paternal and maternal full-sibs and half-sibs. Despite the advantages of these schemes, their success may, however, be hampered by an increase in inbreeding coefficient and loss of genetic diversity in the population, since animals of higher genetic value will be widely used in the Nucleus and in commercial herds, in detriment of others. In the case of the MOET Nucleus scheme, the risks are even greater, since much of the replacement of the parents is done throughout the selection process with individuals from the Nucleus itself, or related to the founding and successive generation parents. The objective of this project, therefore, was to develop instruments to monitor and control the genetic diversity and the inbreeding coefficient in the herds under selection for dairy production participating in the Guzerá breeding program. For that purpose, taking into account genealogy and DNA marker data of the animals studied in the program, the genetic variability, effective size, inbreeding coefficient, population structure, bottleneck effect, genetic distance, allelic frequencies, heterozygosity, PIC (content of polymorphism information) and Hardy-Weinberg equilibrium were evaluated using some microsatellite loci information. The genealogic data were collected in databases stored in Embrapa/CBMG2/ABCZ (Brazilian Association of Zebu Breeders) deriving from 15 dairy herds, distributed in different regions of the State of Minas Gerais. Great part of the molecular data was obtained from the DNA Bank of the Guzerá breed, under the curatorship of the Molecular Genetic Laboratory of Embrapa Dairy Cattle, and additional data were collected when this research work started, in order to improve the precision of the study. The results, in this way, are likely to effectively contribute for the sustainability and continuity of the National Dairy Breeding Program for the Guzerá Cattle.