The difference between measles and smallpox is large, mainly focusing on the level of pathogenesis, pathogenic mechanism, clinical symptoms and so on. 1. Pathogenesis: Measles is an acute respiratory infectious disease caused by measles virus, which belongs to category B infectious disease in China’s statutory infectious diseases. Smallpox is a virulent infectious disease caused by smallpox virus infection, which is highly lethal but has been eliminated by human beings. 2. Pathogenesis: both can be transmitted by respiratory droplet transmission and close contact. Smallpox virus has higher transmissibility and pathogenicity, and the lethality is much higher than that of measles. For measles, if there is no immunity to measles virus, more than 90% of the population can develop after exposure to the virus, generally without complications, and after the disease can obtain lasting immunity; but smallpox disease develops rapidly, and the mortality rate of the unimmunized population in a short period of time can be as high as 30%. 3. Clinical symptoms: after the occurrence of measles and smallpox, the human body will appear a certain red rash, but the time and severity of the maculopapular rash has a big difference. Measles usually appears 3 to 4 days after the onset of fever, while smallpox appears in about 2 to 3 days and is accompanied by severe toxemia, which can aggravate the risk of death.