The synthesis and spectroscopical data of 1,2,6-thiadiazine 1,1-dioxides, designed as antiprotozoal agents, are reported. The in vitro trichomonacidal and trypanocidal activities of new compounds and their precursors were evaluated against Trichomonas vaginalis and Trypanosoma cruzi. The chemoprophylactic activity on mice treated with blood infected with T. cruzi and their mortality percentage were tested. Compounds 2 and 8b show a higher chemoprophylactic activity and lower mortality percentage than Nifurtimox used as reference drug.