Streptococcus suis is a zoonotic pathogen of economic significance to the swine industry. The number of infected cases is increasing in humans worldwide. In this study, we determined the prevalence and diversity of S. suis carriage in slaughterhouse pigs in Phayao province, Thailand, where an outbreak occurred in 2007. The overall S. suis carriage rate was 35.2% among slaughterhouse pigs. The prevalence rates of serotypes 2 and 14 (the major serotypes infected in humans) were 6.7% and 2.6%, respectively. In both serotypes, 70.4% of isolates of serotypes 2 and 14 revealed sequence types and pulsotypes identical to human isolates in Thailand. It is suggested that pathogenic strains of S. suis are a risk factor for occupational exposure to pigs or the consumption of raw pork products. Food safety, hygiene, and health education should be encouraged to reduce the risk group.