Gas gangrene refers to severe necrotizing syndromes in soft tissues of animals caused by Clos-tridium. Five species of histotoxic clostridia are responsible for myonecroses. These agents require a port of entry, such as skin punctures with needles contaminated with bacterial spores. The present case report describes the clinicopathological findings of gas gangrene in a male Quarter horse living in the Brazilian Amazon biome. Clinical examination revealed clinical signs of toxemia and an enlarged left limb. The anamnesis found the administration of medication to this limb. The animal died five hours after its arrival at the veterinary hospital. At necropsy, histopathological lesions characterized by intense muscle necrosis, liquefaction, and gas formation were observed, suggestive of Clostridium lesions, which were confirmed by multiplex PCR. C. septicum was the etiological agent identified.