Abstract： Objective　To observe the immune complex distribution in placenta of intrauterine growth retardation (IUGR). Method　Using immunohistochemical technique (SP method), authors studied the deposition of IgG and IgM in the placenta of idiopathic IUGR patients (including 8 samples of (ACA)-positive and 14 samples of ACA-negative) and patients with Pregnancy induced hypertension (PIH) complicated IUGR. Results　There is no significant difference of IgG deposition in villous vessels among the three groups. The positive rate of IgM in villous vessels、the positive rate of IgG、IgM in decidual vessels and the deposition of IgM in syncytiotrophoblast of both idiopathic IUGR and PIH complicated IUGR were much higher than those of control group (P>0.05). The positive rates of IgG、IgM in decidual vessels and villous vessels between the ACA-positive group and ACA-negative group in the idiopathic IUGR were not significantly different. Conclusions　The immunopathological lesion in placenta might play an important role in the development of IUGR. Idiopathic IUGR and PIH complicated IUGR have the similar placental immunopathological changes. The etiology of IUGR induced by ACA needs more studies.