Abstract: Objective To study the role of cytidine-phosphate-guanosine oligodeoxynucleotide（CpG ODN）on the de-velopment of Plasmodium liver stage. Methods Plasmodium yoelii BY265 18S rRNA was cloned，and the TaqMan real-time PCR was established on P. yoelii BY265 18S rRNA and mouse GAPDH as quantitative analysis model. The model was tested by the level of liver Plasmodium load with the liver cDNA in BALB/c mice infected by salivary gland sporozoites for 42 hours. Twelve BALB/c mice were randomly divided into CpG group，CpG control group and PBS control group which were injected respectively by ODN1826 30 μg，ODN1826 control 30 μg and 0.01 mol/L PBS 200 μl via vena caudalis. Twenty-four hours later，each mouse was inoculated with 100 sporozoites. Mice were sacrificed in 42 hours after infection，and the liver load of Plasmodium was analyzed by TaqMan real-time PCR. Results The cloned Py BY265 18S rRNA gene showed 98% similarity to Py 17XNL. The quantitative analysis model consisted by 18S rRNA and GAPDH showed positive correlation between the level of liver Plasmodium load and the sporozoite inoculation dose to mice. The Plasmodium load in CpG ODN pre-treated mice was reduced to one fifth of the control group（0.28/1.33)（P<0.05). Conclusion The quantitative analysis model of TaqMan RT-PCR can detect the liver load of Plasmodium parasites，and CpG ODN can inhibit the development of its pre-erythrocytic stage.

Key words: TaqMan probe, Real-time PCR, CpG oligonucleotide, Plasmodium yoelii, Pre-erythrocytic stage