en Midwifery Orginal research <strong><em>Background:</em></strong> Mothers in the postpartum period experiences a change in sleep pattern and loss of sleep duration. In the meantime, factors can cause irregular sleep patterns and decreased sleep quality.<br> <strong><em>Objectives:</em></strong> The aim of this study was investigating the factors of fertility, anxiety and physical activity on the sleep quality of the lactating women visiting healthcare centers in Zanjan, Iran.<br> <strong><em>Methods:</em></strong> This descriptive cross-sectional study was carried out from 2018 to 2019 on 380 women aged 14-45 years referred Ayatollah Mousavi Hospital in Zanjan and its affiliated clinics who were maximally 6 months postpartum and selected by convenience sampling method. The measuring tools used in this study included Petersburg Sleep Quality Questionnaire, Beck Anxiety Inventory, and a checklist containing demographic-fertility. Data were analyzed through SPSS software using descriptive and analytical tests (t-test, Mann-Whitney, and Chi-square). The statistical significance level was considered as p<0.05.<br> <strong><em>Results</em></strong><strong>:</strong> in this study 45.8% (n= 174) of the participants suffered from mild anxiety and 13.2% (n= 50) of them from moderate anxiety. The mean score of their sleep quality was 4.70&plusmn; 3.06. The effect of physical activity (p-value= 0.006) and anxiety level (p-value= 0.002) on women&#39;s sleep quality was statistically significant.<br> <strong><em>Conclusion:</em></strong> The results of the present study confirm the positive effect of regular physical activity and the negative effects of anxiety on sleep quality of the breastfeeding mothers. sleep quality, postpartum, anxiety, physical activity, reproductive variables 39 45 http://nmcjournal.zums.ac.ir/browse.php?a_code=A-10-33-8&slc_lang=en&sid=1 Samaneh Youseflu s.yoseflu@yahoo.com 10031947532846007352 10031947532846007352 No Instructor, Department of Midwifery, School of Nursing and Midwifery, Zanjan University of Medical Sciences, Zanjan, Iran Zeynab Bayat zeynab.bayat139022@gmail.com 10031947532846007353 10031947532846007353 No MSc, Student of midwifery at Tehran University of Medical Sciences, Tehran, Iran Faezeh Amiri amirim7676@gmail.com 10031947532846007354 10031947532846007354 No BSc, Midwifery in Ayatollah Mousavi Hospital in Zanjan, Zanjan, Iran Parvin Mohebbi p.mohebbi11@gmail.com 10031947532846007355 10031947532846007355 Yes Instructor, Department of Midwifery, School of Nursing and Midwifery, Zanjan University of Medical Sciences, Zanjan, Iran