Maternal asthma confers the greatest risk for adverse respiratory outcomes in their offspring, notably, an increased incidence of infant wheeze, recurrent bronchiolitis and childhood asthma^{(Reference Mattes, Murphy and Powell1,Reference Morten, Collison and Murphy2)} ; yet there are no prevention strategies in place. Breastfeeding is associated with a reduced risk of wheeze, bronchiolitis, and associated healthcare use in the first 12 months of life in children at high risk of developing wheeze and asthma due to family history of asthma or atopy.^{(Reference Harvey, Murphy and Whalen3)} Thus, supporting breastfeeding in women with asthma may prove an effective approach to the primary prevention of adverse respiratory outcomes in their children. However, our work has shown that women with asthma have lower rates of breastfeeding initiation and exclusive breastfeeding, and early cessation^{(Reference Harvey, Murphy and Gibson4)} compared to both national recommendations and the general population.⁽⁵⁾ Despite substantial potential, no research has addressed the barriers to breastfeeding in this group of women. In women with asthma, this study aims to: (1) quantify breastfeeding rates in the first 6 months postpartum; and (2) characterise the barriers/difficulties to breastfeeding in the first 6 months postpartum. Women with mild asthma recruited into the Breathing for Life Trial Nutrition Study (BLTNUT) were followed through pregnancy and postpartum. Data were collected on infant feeding at approximately 4–6 weeks and 6 months postpartum. One-hundred-and-eighty-five women with asthma completed a post-partum visit: at 4–6 weeks (n = 153), 6 months (n = 154), or both time points (n = 122). One-hundred-and-seventy-four (94%) participants initiated breastfeeding. Of 153 participants who completed a 4–6-week visit, 64.7% were still breastfeeding (either exclusive or partial) at this timepoint. Of 154 participants who completed a 6-month visit, 39% were still breastfeeding. One-hundred-and-thirty-six participants (73.5%) reported at least one barrier to breastfeeding in the first 6 months. Barriers were categorised broadly under Maternal (n = 108), Infant (n = 112) and Feeding-related (n = 72) issues. The leading sub-category was Breast/Nipple-Related issues (n = 89) under the Maternal category, Attachment Issues (n = 74) under the Infant category and Equipment/Assistance Required (n = 34) under the Feeding-Related category. Our data, the first of its kind in mothers with asthma, indicates that barriers to breastfeeding are highly prevalent, affecting three in four women with asthma. Common barriers are amendable to interventions/support services if directed appropriately. However, there are indications of barriers unique to this group e.g. medication concerns. Further research is needed to inform tailored and scalable approaches to facilitate breastfeeding in this group with the aim of protecting maternal and infant health.