OBJECTIVES: To study whether Serum MBPOS-100 can be the sign of early diagnosis in brain injury caused by intrauterine infection. METHODS: The pregnant rats were randomly divided into 2 groups: control group (n=10) and experimental group (n=37). The experimental pregnant rats were consecutively injected LPS 500 mu g/kg center dot d into abdominal cavity at embryonic day 18 in following 2 days. As controls, 10pregnant rats were injected normal saline into abdominal cavity with the same dose at the same time. After delivery, mother rats of both groups were sacrificed and infection station of uterus and placenta were then observed by HE staining. Twenty control rats and 20 experimental rats (7days) were selected randomlyythe changes of ultrastructure in internal capsule, hippocamp, cortex and callus were observed and MBPOS-100 in serum and brain tissues were detected by ELISA method. Data are presented as mean and standard deviations (+/- S) and analyzed with t-test by SPSS11.5 software. RESULTS: Internal capsule of experimental groupyin neuron kytoplasm,chondriosome vacuolar degeneration was diffused,perinuclear space was widen (EMx20K); Cortex of experimental groupyNerve fibers twisty vacuolus appear in nerve ending0Synaptic membrane fuse and synaptic vesicle disappearythe quantity of medullary sheath reduce (EMx20K). Compared with the control group, the content of serum MBP was obviously higher, while lower in brain tissue in experimental group, both had significant difference between the two groups (t=5.1205, p=0.01; t=3.2207,P<0.01); The content of S-100 in experimental group is obviously higher than in control group both in the serum and brain tissueyand also had significant difference(t=5.791,P<0.01;t=4.1543, P<0.01). CONCLUSIONS: Serum MBPOS-100 can be the sign of early diagnosis in brain injury.