Anxiety disorder is one of the most common psychological diseases in postpartum period. This study is designed to assess the relation between maternity blues and postpartum anxiety among Iranian pregnant women In this prospective study, 310 pregnant women (37-40 weeks of pregnancy) who fitted inclusion criteria and had informed consent were selected using convenience sampling method. Demographic and obstetric characteristics and Spiegelberger anxiety questionnaire was complete for each participant. In the first stage, 3-10 days after labor all cases were screened for maternity blues using Stein maternity blues questionnaire, then divided in to two groups with and without maternity blues. In the second stages, 4-6 weeks after labor the prevalence of postpartum anxiety was assessed using Spiegelberger questionnaire. There were significant relations between maternity blues and postpartum Trait anxiety (RR=6.8, CI= 3.6-12.5, P<0.001) and maternity blues and postpartum state anxiety (RR=7.5, CI= 4.1 -13.8, P<0.001). This study confirmed that the incidence of anxiety is more among women with maternity blues at 4-6 weeks postpartum. Given these findings, it is recommended to carefully follow mothers with maternity blues in order to identify women prone to progression of anxiety and their subsequent treatments.