Abstract: Relaxin （ＲＬＸ） is one of the members of insulin superfamily, which play important roles in normal pregnancy maintenance and labor initiation. In females relaxin is produced mainly by the corpus luteum. RLX and its receptor, family peptide receptor relaxin （ＲＸＦＰ１） are widely distributed in ovary, endometrium, deciduas, placenta and fetal membranes. RLX regulates the development of embryo, mammary gland and uterus, the maintenance of pregnancy, cervical ripening, labor initiation and maternal cardiovascular adaptation to pregnancy. Abnormal expressions of relaxin are related to higher incidences of pathologic pregnancies including abortion, preterm birth, premature rupture of fetal membranes, hypertensive disorders in pregnancy and fetal growth restriction. RLX and its receptor, RXFP1 acts important roles in the cytokine regulation network in the maternal-fetal immune tolerance. So far, RLX is known as a multi-effective and promising hormone that participates in much physiological and pathologic process in liver, kidney, heart and brain besides productive system. This review is focused on summarizing the recent advances of researches in the roles for RLX in physiological and pathologic pregnancies.