Aim To prepare and identify monodonal sntibody (Mab) specific for Toaoplasma gondii tachyzoites. Method The Mab specific for Taxoplasma gondii tachyrzoite were prepared via bybridoma technique. Indirect ELISA was used to determine the activity of the Mab. Agarose double immuodiffusion test was performed to confirm subclass and SDS-PAGE & western blot were used to analysis rolecular weight of the antigen (s) recognized by the Mab. IFA was used to identify the epitope of Taxoplasma gondii tachyzoites. The protection and specificity of the Mab were snalysed at same time. The Mab was tesed in Mab-ELISA method to detect Taxoplasma gondii antigen. Results A Msb F7C8H12 specific for T. gondii was produced. It belongs to IgG1 subclass. Moleculsr weight of the sntigens recognized by the Mab was 16.5 and 24 kDa. IFA did not show fiuorescence in intact tachyzoite.Inhibition test showed that the inhibition rate was 50% when the concetration of the antigen was 40μg/ml.Afterthe RH strain tachyzoites were incubated with Mab ascites, mice were inected with the tachyzoites through peritoneum. The results showed that the mean dead time of mice were not delayed. T. gondii antigen mixed with PBS snd normal human serum was detected by Mab-ELISA, the sensitvity was 0.78 yg/ml and 1.5μg/ml respectively. When mice were infected with T. gondiiRH strain tachyzoites, 103/mouse p.i., circulating antigen could be detectedin 6 day and 8 day. Conchusion The Mab (F7C8H12) to T. gomdii tachyzoites is an excellent probe for studying T. gondii snd toxoplasmosis.