Severe viral disease was observed on potato crops growing in Assiut governorate, Upper Egypt. Serological and Molecular identification proved the causal pathogen of this disease is Potato virus Y. comparison of nucleotide and amino sequences of coat protein genes of PVY isolate from Assiut (Upper Egypt) and PVY worldwide isolates revealed that PVY-Assiut shared the highest identity with PVY-NTN isolates and this identity was up to 99% at nucleotide level. Phylogenetic analysis confirmed this close relationship among PVY-Assiut and PVY-NTN strain. These data provided a proof that PVY-Assiut is a PVY-NTN strain. PVY-NTN occurrence has been reported before in North of Egypt but this is the first time to be reported in South of Egypt (Upper Egypt). These data proved the wide spread of this virus all over Egypt and indicated to this strain is replacing the old PVY stain especially PVY-O, PVY-N and presents a serious threat to potato production in Egypt. This study proposes that using nucleotide and amino acid sequences of coat protein gene is a potential tool for identification of PVY strains.