In order to evaluate the trend in the prevalence of porcine reproductive and respiratory syndrome on farms, 25 porcine reproductive and respiratory syndrome virus (PRRSV) strains were collected from 2009 to 2012 from 11 districts in the Guangdong province. The complete gene sequences of NSP9 from the 25 PRRSV strains were amplified, sequenced, and then compared with the published sequences of other strains. The results showed that these sequences shared 97.6-99.4 % of the same nucleotides and 97.5-99.4 % of the same amino acid sequence identities with JXA1, 91.4-93.1 % of the same nucleotides and 95.4-92.6 % of the same amino acid sequence identities with VR2332, and 95.1-98.4 % of the same nucleotides and 95.3-97.0 % of the same amino acid sequences with the classical Chinese vaccine strain Ch-1a. Phylogenetic analyses showed that all of these 25 strains belonged to the North American genotype and were further divided into three sub-genotypes. This basic data allowed us to evaluate the prevalence of PRRS in the Guangdong province and the variation and evolution of the nsp9 gene in PRRSV.