Syphilis is contagious. Syphilis is classified as a Class II infectious disease and is transmitted mainly through sexual contact, vertical mother-to-child transmission and blood transmission, with sexual transmission being the most important route of transmission and very contagious. Syphilis patients have a large number of syphilis spirochetes on the surface of the mucous membrane damage, and it is easy to transmit the virus to each other through the mucous membrane damage during sexual intercourse. Pregnant women with syphilis can also transmit the virus to their babies through the placenta. Syphilis can also be transmitted by sharing syringes with a person with syphilis or by directly injecting the blood of a person with syphilis, or, in a few cases, by kissing, breastfeeding, or touching household items used by a person with syphilis. The intensity of syphilis infection decreases over time and is generally most contagious within one year of infection without treatment. For the prevention of syphilis infection, first of all, we should avoid promiscuous and unclean sex, try to be clean, stay away from drugs, avoid using toilets in public places as much as possible, and avoid irregular injections and blood transfusions. Also pay attention to and reduce daily contact with syphilis patients, do not share clothing and household items, and undergo syphilis screening before marriage.