Highly pathogenic avian influenza (HPAI) subtype H5Nx viruses of the A/Goose/Guangdong/1/1996 (Gs/Gd) lineage have led to substantial economic losses within the poultry industry and represent an ongoing public health threat [1]. The Gs/Gd lineage H5 viruses not only have evolved into ten primary clades 0-9 with their subclades but also reassorted with other influenza A viruses [2; 3; 4]. Notably, since 2020, clade 2.3.4.4b HPAI H5N1 viruses have caused outbreaks across a broad geographic range, including Asia, Europe, Africa, North America, South America, and Antarctica [5; 6; 7]. The infections of HPAI H5N1 viruses in mammals including wild, domestic and humans underscore the potential zoonotic risk and pandemic potential of these evolving H5 viruses [8].In South Korea, the H5Nx clade 2.3.4.4b HPAI viruses caused multiple outbreaks. During October 2022-March 2023, a total of 16 different genotypes of H5N1 2.3.4.4b HPAIV, the Kor22-23A-P, were reported in wild birds, showing a high genetic diversity of clade 2.3.4.4b HPAIVs generated through frequent reassortment with other influenza A viruses [9]. During December 2023-May 2024, H5N1 and H5N6 2.3.4.4b HPAI viruses were reported [10; 11] including 32 cases in poultry farms (home.kahis.go.kr) and 19 cases in wild birds (http://wadis.go.kr). No HPAI virus had been detected in South Korea since June 2024, despite large-scale active surveillance targeting both wild birds and poultry. Here, we report the detection of H5N1 HPAI viruses isolated from a captured wild Mandarin duck (Aix galericulata) on October 15, 2024, and a Northern pintail (Anas acuta) found dead on October 17, 2024, during early-stage HPAI surveillance in fall migration of wild waterfowl into South Korea. To facilitate timely information sharing, we conducted complete genome sequencing of the H5N1 viruses using Illumina next-generation sequencing (NGS) technology and submitted the genome sequences to the GISAID database (https://www.gisaid.org). A comparative phylogenetic analysis was carried out to determine the virus´s origin and genotype.