Background. When researching crop genetic diversity, including flax species, molecular markers are used to identify cultivars, establish phylogenetic relationships among them and select valuable genotypes and sources of useful traits. One of the effective ways to solve these tasks is the use of SSR markers, as a molecular method. The aim of this work was to study the molecular genetic polymorphism of modern flax cultivars listed in the State Register for Selection Achievements of the Russian Federation, find out their phylogenetic relationships and develop a version of their genetic certification.Materials and methods. The materials for the research were 82 flax cultivars (60 cultivars of fiber flax and 22 of oilseed flax) and 3 ancient landraces. Genetic analysis was carried out using the PCR method with a set of 11 SSR markers labeled with fluorescent dyes, followed by the detection of products on the genetic analyzer.Results. The study of the cultivars revealed 50 alleles at 11 loci, with the number of alleles per locus ranging from 2 to 10, averaged to 4.55 alleles per locus. Each flax sample contained a unique set of alleles.Conclusion. The resulting SSR database made it possible to develop genetic certificates for each cultivar in the form of an alphanumeric code. A cluster analysis was also carried out and a dendrogram of genetic similarity was constructed. The identified sib relationships among the cultivars confirmed the information about their origin.