Background: Postpartum anaemia adversely affects maternal mood, cognition, and maternal-infant interactions. Intravenous iron isomaltoside is effective and safe for non-pregnant patients with iron deficiency anaemia, but data on its use in Hong Kong women during peripartum period are limited. This study aims to determine the effectiveness and safety of iron isomaltoside (Monofer) in women with postpartum haemorrhage or anaemic symptoms. Methods: Records of women who received iron isomaltoside (Monofer) when haemoglobin (Hb) level was <7g/dL (or ≥7g/dL when concomitant with anaemic symptoms) irrespective of mode of delivery between April 2018 and March 2021 were reviewed. Primary outcome measures included response to iron isomaltoside treatment (measured by pre-and post-treatment Hb levels), resolution of anaemic symptoms, and the number and types of adverse reactions related to treatment. Secondary outcome measures included associations between patient characteristics and Hb response. Results: 126 women were included for analysis. Most were nulliparous, delivered vaginally, and had minor postpartum haemorrhage. Most had a baseline Hb level of <10.0 (mean, 7.36) g/dL, but only 53.2% of them had anaemic symptoms. No women experienced serious adverse events. Only four (3.2%) women had mild adverse events of rash (n=3) or pruritis (n=1). At the 6-week follow-up, the mean Hb level increased 4.39 g/dL to 11.8 g/dL (p<0.001), with only one woman reporting anaemic symptoms. 12 (9.5%) of 126 women had some form of haemoglobinopathy (usually thalassemia trait) and had lower Hb levels even before pregnancy. Compared with women with normal Hb pattern, women with haemoglobinopathy had lower post-treatment Hb responses (p=0.001). Hb response was positively associated with delivery blood loss (r=0.188) and negatively associated with baseline Hb level (r= -0.279). Conclusion: Iron isomaltoside (Monofer) is effective and safe for postpartum anaemia. It enables rapid improvement in Hb level and anaemic symptoms, even for those with haemoglobinopathy.