Information about viruses affecting potato in South Korea is limited. To fill in this knowledge gap, we conducted a small survey of potato viruses in seed potato grown in South Korea. In 2017, potato plants of five cultivars exhibiting foliar mosaic, crinkling and mottle were sampled in two seed potato production areas, in Gangwon-do and Jeollabuk-do Provinces, and subjected to virus testing and characterization. Potato virus Y (PVY) was found associated with mosaic symptoms, and samples were molecularly characterized. All analyzed PVY-positive samples were found to represent the same recombinant PVY strain: PVY^NTN. Three South Korean PVY isolates were subjected to whole genome sequencing using overlapping RT-PCR fragments, and all three were confirmed to represent strain PVY^NTNa after a recombination analysis of the complete genomes. In phylogenetic analysis, the three South Korean isolates were placed most closely to several PVY^NTNa isolates reported from Japan and Vietnam, suggesting a common source of infection. This is the first report and complete molecular characterization of a PVY^NTN strain present in South Korea, and since this strain induces tuber necrotic ringspot disease in susceptible cultivars of potato, appropriate management tools need to be implemented to mitigate potential tuber quality losses.