Aeromonas hydrophila is a facultative anaerobic gram-negative bacterium regarded as an opportunistic pathogen in animals. A 17-year-old female crab-eating macaque (Macaca fascicularis) died after experiencing anorexia and depression for several days. The carcass was severely emaciated, and the sternum was exposed under subcutaneous lesions in the thorax. Many abnormal pathological lesions were found, including tracheal inflammation, pulmonary inflammatory emphysema, yellowish discoloration of the liver, enlargement of the gall bladder, necrosis of the heart, congested bilateral kidneys, and enlargement of the adrenal glands. The stomach was empty, mucosal ulcerations were found, and the duodenum was congested. Giemsa staining revealed rod-shaped organisms in the whole blood smear and major organs, which were identified as A. hydrophila. The animal had experienced stress, and decreased immune system function possibly contributed to the infection.