Objective To investigate the infectivity of serum and vaginal fluid in early cases and late latent cases of syphilis. Methods From January 2015 to December 2015, sixty-eight female patients with latent syphilis were enrolled in the outpatient clinic of Ningbo Women and Children′s Hospital, including 38 early cases and 30 late cases. Tolulized red unheated serum test (TRUST) was detected by using kits and Treponema Pallidum DNA (TP-DNA) was detected by polymerase chain reaction. TP-DNA levels in serum and vaginal fluid were compared before and after benzathine penicillin treatment in patients with early and late latent syphilis. Chi square test was performed for count data analysis. Results TRUST negative conversion cases in early latent syphilis after 3, 6 and 12 months of treatment were 11 (28.9%), 16 (42.1%) and 27 (71.0%), respectively. TRUST negative conversion cases in late latent syphilis after 3, 6 and 12 months of treatment were 6 (20.0%), 12 (40.0%) and 14 (46.7%), respectively. There were no statistical differences in TRUST negative conversion rates after 3 months and 6 months after treatment between early cases and late cases (χ2=0.716 and 0.031, respectively, both P>0.05), while those after 12 months of treatment between early cases and late cases were statistical different (χ2=4.164, P 0.05). The serum TP-DNA positive cases in early syphilis before and after 3, 6, and 12 months of treatment were 18 (47.3%), 4 (10.5%), 5 (13.2%) and 5 (13.2%), respectively, with statistical difference (χ2=21.217, P 0.05). The serum TP-DNA positive cases in late syphilis before and after 3, 6, and 12 months of treatment were 8 (26.7%), 1 (3.3%), 1 (3.3%) and 1 (3.3%), respectively, with statistical difference (χ2=14.712, P<0.05). Conclusions Standard treatment can reduce the level of TP in serum and vaginal fluid of latent syphilis women and improve the negative conversion rate of TRUST. Late latent syphilis is easier to create sero-resistance than early cases. The early cases have stronger infectivity than late cases before standard treatment. Key words: Syphilis, latent; DNA; Treponema pallidum