BACKGROUND Acute mastitis is a common disease occurring in postpartum lactating women. This study aimed to identify the high-risk factors for suppurative mastitis (SM) in women who were breastfeeding. MATERIAL AND METHODS A total of 262 non-SM patients and 63 SM patients admitted to the Department of Breast and Thyroid Surgery of Liaocheng People's Hospital were retrospectively enrolled in this study. The high-risk factors for SM during lactation were determined by assessing admission time after acute mastitis, galactostasis, primipara or pluripara, nipple injuries, antibiotic treatment course, and diabetes. RESULTS The incidence of SM in patients with admission time greater than 72 h after occurrence of acute mastitis was significantly higher than that in patients whose admission time was less than 72 h (p<0.0001). Patients with galactostasis were more prone to develop SM compared to patients without galactostasis (p<0.0001), and the incidence of SM in primiparous patients was significantly higher than that in pluriparous patients (p=0.003). The incidence rate of SM was significantly higher in patients with diabetes than in patients without diabetes (p=0.002). Patients with nipple injuries were more prone to suffer from SM relative to the patients without nipple injuries (p<0.0001). However, there was no significant difference in the incidence of SM according to the antibiotic treatment course (p=0.134). CONCLUSIONS SM during lactation was closely associated with admission time after the occurrence of acute mastitis, galactostasis, primipara, diabetes, and nipple injuries.