The golden cuttlefish () is a rising aquaculture species with high economic value in China. A disease with necrosis symptoms in golden cuttlefish larvae emerged in a hatchery in Huangdao District, Qingdao. In this study, the pathogen was isolated and identified, the histopathology was investigated, and its route of transmission and sensitivity to different antibiotics were tested. The symptoms included anorexia, slow growth, and a dark body. In addition, the skin, muscles, oral arm, tentacular arm, and the internal organs were extensively ulcerated, and the mortality reached as high as 90%. Histopathological analysis showed that the chromatophore and the gill filament structure were disintegrated, the myofilament was broken, a large number of hepatic lobule epithelial cells were necrotized, and the microvilli of intestinal epithelial cells were shed off. Three dominant bacteria (SE-A, SE-B, SE-C) were isolated from the diseased golden cuttlefish larvae. Artificial infection experiments illustrated that the strains of SE-B and SE-C were the causative pathogens with a median lethal dose of 3.98×10⁶ CFU/mL and 8.91×10⁵ CFU/mL, respectively. Based on morphological observations, and physiological, biochemical, and molecular analyses (16S rDNA), SE-B was identified as . The analysis of the transmission route demonstrated that the two pathogens present during golden cuttlefish breeding were mainly carried by . The chemotherapeutant sensitivity tests illustrated that SE-B was sensitive to doxycycline and florfenicol, etc., while it was insensitive to streptomycin and gentamicin, etc. SE-C was sensitive to florfenicol and lomefloxacin, etc., while it was insensitive to neomycin and clarithromycin, etc.