Objective To explore the effect of reducing sub-clinical infections of Toxoplasma gondii in newborn babies with preventive treatment. Methods Forty-four infected pregnant women were treated in different period and their umbilical blood and/or placenta of their newborn babies were tested for IgG, IgM, cAg and DNA of Toxoplasma gondii. Results The positive rate of Toxoplasma DNA in umbilical blood was 37.8%(14/37). The lowest rate was found in the preventive treatment group with a significant difference compared with the group of general treatment. Conclusion Preventive treatment can reduce sub-clinical infection rate of newborn babies effectively.