Hemagglutinin (HA) and neuraminidase (NA) are glycoproteins that play crucial roles in transfaunation, membrane fusion and the release of progeny virions of influenza A virus. Previous reports showed that Nglycosylation of HA and NA proteins are closely related to these properties of the virus. In this study, the authors analyzed the number, position and conservation of N-glycosylation sites on NA of 29 H5N1 virus strains circulating in poultry in Northern Vietnam during the period from 2008 to 2009. Total RNA of each clinical sample was extracted then used as template for full-length amplification and cloning of NA segments of H5N1 virus. The nucleotide sequences of segments were determined by Sanger's method, translated into amino acid sequences and then determined potential N-glycosylation sites of the sequences by using NetNGlyc 1.0 software. The result showed that though 3 potential N-glycosylation sites (68, 126, and 215) in NA are conserved in almost all of H5N1 virus strains, mutations that altered the number and position of potential N-glycosylation sites were found in some H5N1 virus strains.