Streptococcus suis is a common opportunistic pathogen in pigs. S. suis is known as emerging zoonotic pathogen. Human infection with S. suis has been increasingly reported in the recent years, specially in Asia. Diagnosis for S. suis infection is currently carried out with bacterial culture or amplification of the specific DNA, cps2J gene, for serotype 2 from clinical specimens. Amplification for a specific region of 16S rDNA of S. suis to identify S. suis of all 35 serotypes in blood specimen was investigated to determine its limit of detection and specificity for diagnosis purpose. Blood samples of 521 porcine reproductive and respiratory syndrome (PRRS) virus infected pigs were investigated for co-infection of S. suis. The high specificity with a limit of detection of 25 copies/reaction with DNA extracted from blood specimens were determined and 10.6 percent of PRRS sick pigs were identified to be co-infected with S. suis. The study results showed that the specific S. suis 16S rDNA methods can be used for diagnosis of S. suis infection in humans and pigs.