The aim of this study was to investigate the sexual function of mothers at one year postpartum and associated factors. Four hundred and ninety Iranian women were recruited randomly at four time periods from child birth: first 3 months, 4 to 6, 7 to 9 and 10 to 12 months, from January to July 2008. All mothers were married, literate and agreed with participation. The exclusion criteria were, (a) loss of baby, (b) living far from their partner, (c) psychological problems and (d) serious medical diseases. Data on socio-demographic factors, obstetric, medical, last delivery and postpartum history was obtained. The sexual function was evaluated by the 19th item questionnaire of Female Sexual Function Index (FSFI). The mean resumption of intercourse was 57.17 +/- 27.95. Twenty-four had no sexuality. The most common reasons were fear of pain, no interest, worrying about another pregnancy, feeling tired and bleeding. All dimensions of women's sexual function were at the lowest level in early postpartum. Sexual activity had significance correlation with an older maternal age, a longer marriage duration and higher number of children. Mothers diseases, neonate problems and tuboligation were associated with lower scores of sexual function. There was no association with delivery type and perineal injuries. Sexual parameters decrease at the first 3 months of postpartum and recovery during the following months. More consultation and direction of postnatal sexuality recurrence is needed.