Avian influenza virus (AIV) is an enveloped virus with segmented RNA that belongs to the Orthomyxoviridae. Recently, avian influenza virus isolates have not only posed a significant threat to the poultry industry but also serious public health concerns. The full-length viral hemagglutinin (HA), neuraminidase (NA) or both genes were inserted into the yeast Kluyveromyces lactis genome to allow for secreted expression. Both hemagglutinin and neuraminidase activities were demonstrated for the expressed proteins. Based on PNGase F digestion and immunoassays, N-glycosidically linked high mannose or hybrid-type carbohydrate chains on the HA protein are predominant. It is noteworthy that when co-expression of the HA and NA proteins was carried out, the NA protein was able to react with the HA protein, resulting in deglycosylation in a manner similar to PNGase F digestion. Such post-translational modifications in the HA and NA proteins of AIV are described for the first time.