[Objective] It is well accepted that vaccination by oral administration has many advantages over injected parenteral immunization.The present study focuses on whether oral vaccination with a DNA vaccine could induce protective immunity against respiratory challenge infection.[Method] The M1 gene of influenza A virus was used to construct DNA vaccine using pcDNA 3.1(+) plasmid, a eukaryotic expression vector.The cationic liposome, which can greatly enhance the expression of recombinant plasmid due to the protective delivery of functional DNA resisting against DNAse in digestive tract, is used as a delivery vehicle for oral vaccination.C57BL/6 mice were randomized into three groups and vaccinated intragastrically with 100μg lipofectamine-encapsulated pcDNA3.1 (+)/M 1 DNA plasmid,pcDNA3.1 (+) plasmid or PBS three times at weekly intervals.