To elucidate the characteristics of molecular epidemiology of PRRSV in China, the nucleotide sequence of open reading frame 5 (ORF5) coding regions from two wild PRRSV strains, J 1 and S1, isolated in northern and mid-eastern regions of China was determined by RT-PCR. Comparison showed that only 4 different bases between J 1 and S1 strains resulted in 3 amino acid (aa.) changes in their deduced proteins. There were 3 and 2 different aa. between the deduced aa. sequences of J 1, S1 strains and the American prototype ATCC virus VR2332 respectively, while there existed 16 and 15 aa. changes between the 2 isolates and the modified live vaccine strains derived from VR2332. The putative protein molecular weight, isoelect ric point, signal region, glycosylation site and possible transmembrane helices of ORF5 of each strains were similar to that of VR2332 strain. These result s showed that the two isolates belong to the same genotype and they may come from USA.