Abstract: To investigate whether NMMHC-ⅡA was related to the resistance to PRRSV, the partial region of NMMHC-ⅡA gene 954 bp encoding the C-terminal region of NMMHCⅡA protein including 23 amino acid residues bound to PRRSV in hybrid pigs(Duroc×Yorkshire×Landrace), Laiwu and Dapulian pigs was cloned; then its homology with other species，the differences at nucleotide and amino acid sequences level between pig breeds and mRNA expression pattern in porcine tissues were analyzed. The results showed that NMMHC-ⅡA cDNA sequence was highly conservative among mammalian species, NMMHC-ⅡA had high homology with human, rat, mouse, cattle, monkey and dog, respectively at nucleotide and amino acid levels. Alignment of nucleotide sequence of NMMHC-ⅡA gene among Laiwu, Dapulian and Duroc×Yorkshire×Landrace crossbred commercial pigs revealed three nucleotide changes, however, the amino acid sequence was identical. NMMHC-ⅡA mRNA expression was analyzed in different tissues by RT-PCR, its expression level was high in skeletal muscle, lung, liver, kidney, spleen, bronchial lymph node, tonsil, stomach, large intestine, small intestine tissues, low in heart and cerebrum, and nearly undetectable in cerebellum and uterus. The results reveal that there is no differences in the function of NMMHC-ⅡA gene among Laiwu, Dapulian and Duroc×Yorkshire×Landrace crossbred commercial pigs, and it is expressed in many tissues except cerebellum and uterus. The role of NMMHC-ⅡA in resistance to PRRSV requires further study.