After regular treatment of syphilis (6 months after the end of treatment for early syphilis and 1.5 years after the end of treatment for late syphilis), although the RPR titer is reduced, it is never negative, and this situation is called serum fixation reaction. What to do in such a case: First of all, it should be excluded whether the treatment is incomplete, while detailed examination for visceral or neurosyphilis, and if necessary, cerebrospinal fluid RPR test. It is also necessary to consider whether there is a relapse or reinfection. Then the anti-syphilis treatment should be continued in adequate amount and duration. Otherwise, no further treatment is needed, and regular follow-up observation can be performed. If the titer rises during the observation period, consideration should be given to continue anti-syphilis treatment, and for the specific rise, please consult the relevant doctor at the hospital in time.