In 2012-2013, a serious infectious disease characterized by exophthalmia, hemorrhage, and neurological symptoms emerged in farms in Sichuan Province. A Gram-positive, chain-forming coccus was found in liver and kidney smears. Two strains of Gram-positive, chain-forming cocci were isolated from the diseased fish. The colonies had a smooth-surface and were white, circular, regular and pin-head sized after incubation at 28 for 48 h on brain heart infusion (BHI). Artificial infection proved that the isolates were the pathogen of the disease. It was primarily identified to be according to morphological, physiological and biochemical characteristics. Furthermore, a 16S rRNA gene sequence analysis by BLAST in GenBank indicated that the two isolates showed high levels of similarity to (more than 96.5%). A phylogenetic tree was constructed comparing the 16S rDNA sequences of both isolates (GenBank accession number KF773744 and KF761304) to other related bacterial species in the GenBank database. In the phylogenetic tree the two isolates and other strains constituted a branch. In addition, the two isolates were positive in a specific PCR detection of gene. Based on the phenotypic characteristics, phylogenetic analysis of the 16S rRNA gene, and specific PCR detection, both . The sensitivity results showed that both strains were sensitive to doxycycline, amoxicillin, cephalothin V, ofloxacin and levofloxacin, but showed some difference in sensitivity to neomycin and amikacin. Histopathologically, the infection could cause serious pathological changes in multi-organs and tissues, especially in liver, kidney and brain. The main pathologic lesions were degeneration, necrosis and infiltration of the inflammation cells. Electron microscopical examination found that bacteria could invade hepatocytes, renal cells and neurons, causing destruction of mitochondria and endoplasmic reticulum.