Awareness of the danger signs of obstetric complications is the essential first step in accepting appropriate and timely referral to obstetric and newborn care. The objectives of this study were to assess women's awareness of danger signs of obstetric complications and to identify associated factors in a rural district in Tanzania. A total of 1118 women who had been pregnant in the past two years were interviewed. A list of medically recognized potentially life threatening obstetric signs was obtained from the responses given. Chi- square test was used to determine associations between categorical variables and multivariate logistic regression analysis was used to identify factors associated with awareness of obstetric danger signs. More than 98% of the women attended antenatal care at least once. Half of the women knew at least one obstetric danger sign. The percentage of women who knew at least one danger sign during pregnancy was 26%, during delivery 23% and after delivery 40%. Few women knew three or more danger signs. According to multivariate logistic regression analysis having secondary education or more increased the likelihood of awareness of obstetric danger signs six-fold (OR = 5.8; 95% CI: 1.8–19) in comparison with no education at all. The likelihood to have more awareness increased significantly by increasing age of the mother, number of deliveries, number of antenatal visits, whether the delivery took place at a health institution and whether the mother was informed of having a risks/complications during antenatal care. Women had low awareness of danger signs of obstetric complications. We recommend the following in order to increase awareness of danger signs of obstetrical complications: to improve quality of counseling and involving other family members in antenatal and postnatal care, to use radio messages and educational sessions targeting the whole community and to intensify provision of formal education as emphasized in the second millennium development goal.