Breastfeeding is the cornerstone of child and maternal health. However, maternal breast problems during breastfeeding have been frequently reported as one of the reasons for early discontinuation of breastfeeding. Despite the importance of having knowledge on breast problems magnitude and its associated factors in the clinical practices and designing effective interventions, there is limited data on this topic. Therefore, this study aimed to assess the prevalence and associated factors of breast problem among postnatal lactating women in Legambo district, south wollo zone, North East Ethiopia, in 2022. A community-based cross sectional study was conducted among 610 lactating mothers in Legambo district. Multi-stage sampling was employed to select study participants. Interviewer administered, WHO B-R-E-A-S-T-Feeding, observational checklist and maternal self-reported breast problem questionnaires were used to collect the data. Epi-Data version 3.1 was used for data entry and export to SPSS version 25.0 for analysis. Descriptive statistics and bi-variable and multivariable analysis was carried out. On the multivariable logistic regression, variables with p-value < 0.5 were considered as they had statistically significant association with breast problem. The overall prevalence of breast problems among postnatal lactating women was 54.3% (95%, CI 49.3–59.3%). Primipara (AOR = 5.09; 95% CI 3.40–7.62), preterm infant (AOR = 2.12; 95% CI 1.22–3.66), home delivery (AOR = 3.67; 95% CI 1.62–8.30), ineffective breastfeeding techniques (AOR = 2.45; 95%CI 1.61–3.74), caesarean section delivery (AOR = 2.05;95%CI :1.15–3.64) and mixed type of feeding (AOR = 1.97:95%CI 1.34–2.89) were factors showed significant association. The prevalence of breast problems was 54.3%. Relevant factors related to an increase risks are being primipara, cesarean section delivery, home delivery, preterm birth, ineffective breastfeeding techniques and mixed type of feeding.