The complete genomes of porcine reproductive and respiratory syndrome virus (PRRSV) strains LX and JX were cloned and sequenced. The complete genomes of LX and JX in length were 15,412 bp and 15,320 bp excluding the poly A, resp. Compared with other reference strains, such as JXA1, VR2332, CH-1a, BJ-4 and LV, the sequence identities of PRRSV JX strain were 91.1%, 98.6%, 91.0%, 94.6%, 90.9% and 61.7%, resp.; the sequence identities of PRRSV LX strain were 91.1%, 89.7%, 99.7%, 91.5%, 99.7% and 62.2%, resp. The comparison for the nucleotide sequences of 5'-untranslated region (5'-UTR), nonstructural protein Nsp2 and open reading frame ORF2-6 from different isolates showed that the maximal mutation sites were Nsp2 and ORF5 from North American strain of PRRSV. North American strain of PRRSV could be divided into four subgroups according to the nucleotide sequence of 5'-UTR, LX strain and JX strain belonged to classical American type and "hyperpyrexia disease" mutation type, resp. On the basis of the nucleotide sequences of Nsp2 and ORF5, North American strain of PRRSV could be divided into five subgroups, and PRRSV JX strain was independent.