Abstract: Objective: To observe the relationship between newborn mice interstitial pneumonia and Ureaplasma urealyticum(UU) infection during the period of pregnancy of a vertical transmission animal model by genital infection with UU during the course of cyesis.Methods: Pregnant mice were infected by blood serum type 4 UU through vagina,interstitial pneumonia and settlement of UU in the newborn mice were observed by the methods of UU culture,pathology and immunohistochemical staining test;at the same time,control group was established.Results: Pathological examination showed that interstitial pneumonia occurred in the newborn mice of experimental group and its spleen had multinucleated giant cell,the lung and spleen of newborn mice had field planting of UU by etiology examination.In experimental group,UU positive detection rates in 356 neonatal mice lung and spleen were 33.34% and 71.36%,respectively;while UU were not detected in cultures from 378 above-mentioned tissues in control group;there were also plenty of UU antigen in the lung and spleen of newborn mice by immunohistochemical staining test;while control group had no phenomenon.Conclusions: The experiment demonstrates that the infection of UU during the period of pregnancy could influence embryonic development through vertical infection and result in newborn interstitial pneumonia.