Abstract: Infectious agents during pregnancy are very important not only threatening maternal health, but also causing fetus death and congenital disorders. It was decided to have serologic study of the infectious agents (Listeria monocytogenes, Mycoplasma, cytomegalovirus and rubella) Leading to abortion in women. This descriptive study was done on 150 pregnant women age range of 26.35�4.85 years with spontaneous fetus death in early months of pregnancy and referring to Imam Khomeini hospital for abortion. In this study two blood samples of each 7ml were drawn on the first day of referring and after two weeks for determining of antibody titer against listeria monocytogene, Mycoplasma, rubella and cytomegalovirus by ELISA, cold agglutination, direct and in direct immunofluorescence methods using Diagnostic kit from Erma Company. In this study, 16% had 5-fold higher antibody titer against Listeria monocytogenes, 42%, 1.5 to 5-fold higher for rubella; 6%, 2.5-4 fold for Listeria monocytogenes and 9% 1.5 to 2-fold higher for cytomegalovirus. All of them in the repeated examination showed higher antibody titer. Fetus death was observed during different stages of pregnancy in the women positive antibody for Listeria monocytogenes, cytomegalovirus and rubella. In 80% positive Listeria monocytogenes antibody fetus death occurred on the end of the second trimester (week 23-26). Since the infectious agents have very important role in fetus death, knowledge of the pregnant women on the prevention method and using of correct method is very important.