Abstract: In order to investigate the pathogen of acute death occurred of piglets from pig farms in Guangdong province and the phylogenetic position, six strains of alpha hemolytic bacteria were isolated from sick piglets with acute death in pig-rearing farm in Yingde, Longmen, Wongyuan, Shantou regions of Guangdong province. Morphological observation, biochemical identification, drug sensitive test, pathogenicity test and sequence analysis of 16S rRNA genes confirmed the six stains of alpha hemolytic bacteria as porcine green gas aureus, designated HD, WY, ZQ, LM, YD and ST, independently. Pathogenicity test showed that, the six isolates had different degree of pathogenicity. The results of drug sensitive test indicated that, the six isolates were highly sensitive to ceftriaxone, cefazolin, enrofloxacin and amoxicillin, moderate sensitive to novobiocin, rifampin, amikacin gentamicin and polymyxin B, resistant to other antibiotics. Homologic and phylogenetic analyses indicated that, the six isolates shared identity above 93% with 12 reference strains at the nucleotide level, with the highest identity 98.1% to strain 15MS from dog in Australia, and the lowest identity 83.6% to strain GXBL- 1 from pig in Guangxi; The six isolates clustered with strains from Guangdong and Australia, suggesting that evolution did not exist obvious regional correlation. This study confirmed the pathogenic bacteria causing acute death of piglets in large scale pig farm, and provided the basis for prevention and cure of disease caused by the bacteria.