Objective To study decontamination technique of caesarean section among flagellates infected transgenic mice，and to establish specific pathogen-free ( SPF) mice strain in order to provide technical support for establishment of flagellates-eradication methods of genetically engineered mice． Methods APPswe /PS1dE9 transgenic mice ( APP mice) were used to conduct this research． Caesarean section was taken on pregnant APP mice to get pups under a SPF barrier environment，and the pups were transferred to female SPF Parkinson's Disease transgenic mice which served as a foster mother． Survival rates of pups were calculated in 7 days of age and after weaning． Pathogens were tested in the first month，and later，every 3 months since Caesarean sections． APPswe gene of APP mice was amplified by polymerase chain reaction ( PCＲ) for genotyping． Average gene positive rate was calculated among the pups and their offspring ( F1) ，and one sample t test was conducted to compare the average gene positive rate with the theoretical Mendelian segregation ratio ( 50% ) ． Ｒesults We performed 11 Caesarean sections on APP pregnant mice，and a total of 75 pups were collected and transferred to a foster mother． Survival rate of the pups after 7 days and weaning was 90. 67% ( 68 /75) and 73. 33%( 55 /75) ，respectively． Pathogens tested before decontamination showed flagellates infection among APP mice was 100% ( 5 /5) ，but after decontamination，all the pathogens required for SPF all show negative results． The average APPswe gene positive rate of the dams in APP mice after decontamination was 48. 3% ，which was in accordance with the Mendelian segregation ratio ( P ＞ 0. 05) ． Conclusion We had successfully eradicated flagellates from the APP mice by caesarean section and a foster mother technique with stable hereditary feature of APPswe gene．