This review is conducted to highlight the application of molecular genetics for improvement of diseases resistance in livestock. Diseases prevention is a serious issue to restrict economic damage due to economically important diseases outbreaks worldwide. Over the last decades, the excessive use of drugs has been criticised because of the possible development of drug-resistant zoonotic organisms and the potential dangers of drug residues in food animal products for human consumption. To prevent this problem following the ways for host resistance improvement to disease is a low cost and sustainable approach. So, this literature review was done on the theory of how to use molecular markers to select for quantitative trait loci (QTL) in genetic improvement programs, both within populations and for introgression of QTL from one population to another. If the effect of each marker is known, then an animal with no available phenotype for disease can be genotyped and its direct genomic value can be estimated based on its genotype only. The advantage of such a method is that accurate estimates of genetic merit can be achieved exploiting knowledge of the genotype of the animal even if the animal is very young. So, it is possible to put recommendation for further research on the generation of phenotypes that are resistant to diseases and development accurate bio-markers that can be readily measured in large numbers of animals at a relatively low cost.