The aim of the study is to verify the knowledge and practices of health professionals working in prenatal care (PNC) related with syphilis during pregnancy and to identify the main barriers to the implementation of protocols for the control of this disease. METHODS: cross-sectional study in Teresina, Brazil, from January to May 2015, 2 conducted with 366 physicians and nurses working in PNC, corresponding to 70% of eligible professionals. We evaluated twenty knowledge and practice criteria related to the diagnosis and treatment of syphilis during pregnancy with a 95% compliance standard. We performed descriptive analysis of the data and used chi-square statistical test to verify differences according to professional category. Results: Only two criteria "knowledge about Mother to Child Transmission according to gestational age" and "counselling on infection" reached 95% compliance. Knowledge of the epidemiological profile of congenital syphilis (CS) and the goal of elimination of CS and knowledge about serological tests had scores below 50% while practices related with post-test counselling, cure control and treatment of partners reached 60%. We identified organisational barriers related to the late initiation of PNC and the delayed return of syphilis test results, to the application of Benzathine penicillin in primary care units and the treatment of partners. CONCLUSIONS: Strategies for early initiation of PNC, implementation of rapid tests for syphilis, ensuring treatment of pregnant women with penicillin, adequate partner treatment and continued education of health professionals on clinical management and counselling in sexually transmitted diseases are necessary to eliminate congenital syphilis.