Mothers who are employed postpartum are less likely to continue breastfeeding than mothers who are not formally employed. However, as postpartum employment is increasingly necessary for the majority of new mothers, it is important to investigate factors that influence the continuation of breastfeeding in employed mothers. A sample of 1,738 mothers who returned to paid employment postpartum were recruited from the obstetric units of four public hospitals in Hong Kong, and prospectively followed for 12 months or until their infant was weaned. More than 85 % of participants returned to formal employment within 10 weeks postpartum, with over 90 % of these employed full-time. About one-third of the participants (32 %) were able to combine breastfeeding and employment, with breastfeeding defined as continuing for more than 2 weeks after returning to work postpartum. Later return to work and higher maternal education were associated with new mothers being able to combine breastfeeding and employment. Later return to work, shorter working hours, parental childcare, and higher maternal education were also associated with less likelihood of weaning from any or exclusive breastfeeding. Improvements in employment-related conditions for mothers and additional support for lower educated mothers may be effective strategies to enable employed women to continue breastfeeding after their return to work.