Feverish mouth ulcers can be seen in viral infections, recurrent aphthous ulcers, syphilis, etc., and should be promptly consulted and treated. 1. Viral infections can be seen in herpetic isthmus, which is caused by enteroviruses such as coxsackievirus A and enterovirus 71, manifested by fever, sore throat, cough, herpes in the pharyngeal isthmus, which is highly contagious. 2. Recurrent aphthous ulcers may be related to psychological factors, immunologic factors, genetic factors, and environment. It manifests as deep and large ulcers, localized burning pain, often accompanied by malaise, low-grade fever, enlarged lymph nodes and so on. 3. Syphilis is a sexually transmitted disease, mostly appearing in the second stage of syphilis, manifested as a generalized syphilitic rash of red or reddish-brown papules, which can also be manifested as oral ulcers, genital ulcers, etc., accompanied by fever. 4. Leukosis is a chronic systemic vasculitis, manifested as systemic ulcers, such as oral ulcers, genital ulcers, but also can be manifested as low fever, erythema nodosum. Feverish oral ulcers can be seen in a variety of situations, if not actively treated, may have serious consequences, so should promptly seek medical attention, standardized treatment under the guidance of a doctor.