Crown rust, caused by Puccinia coronata f. sp. avenae, is one of the most destructive fungal diseases of oat worldwide. Growing disease-resistant oat cultivars is the preferred method of preventing the spread of rust and potential epidemics. The object of the study was Pc59, a race-specific seedling crown rust resistance gene, highly effective at all growth stages. Crown rust reaction tests were performed and the proportions of phenotypes in segregating populations derived from a cross with two crown rust susceptible Polish oat cultivars, Kasztan × Pc59 and Bingo × Pc59, confirmed monogenic inheritance of the gene. Effective gene introgression depends on reliable gene identification in the early stages of plant development, thus the aim of the study was to develop molecular markers tightly linked to Pc59. Segregating populations of Kasztan × Pc59 and Bingo x Pc59 were genotyped using DArTseq™ technology based on next-generation Illumina short-read sequencing. Marker associated with Pc59 were located on chromosome 7D of the current version of the oat reference genomes, Avena sativa OT3098 v2 [1] in the region between 306,171 and 306,689 bp and Avena sativa cv. Sang [2] in the region 738,878 and 739,392 bp . Based on SNPs discovered in this area allele-specific marker was subsequently developed. Marker co-segregated with the Pc59 resistance/susceptible alleles were mapped to the partial linkage group at 0.6 and 6.0 cM, respectively. The newly developed co-dominant marker will be a valuable tool for marker-assisted selection in breeding programs and may be useful for oat mprovement.