BackgroundMastitis and accompanying pain have been associated with the cessation of breastfeeding. Mastitis is an inflammatory condition of the breast and may be a result of decreased immunity and a lowered resistance to infection. Mastitis affects up to one in five breastfeeding women with most episodes occurring in the first 6–8 weeks postpartum. Antibiotics are often used in the treatment of mastitis, but have not been popular or proven effective as a preventative agent. The WHO has highlighted significant concerns relating to adverse harms of antibiotic use with the production of antibiotic-resistant strains of disease organisms. Increasing research suggests that specific probiotic bacteria possess significant anti-inflammatory properties and supports their potential use as immunomodulatory agents. While animal studies have shown promising results in the use of probiotics for preventing mastitis, their use in human trials has had limited investigation. The aim of this study is to evaluate the effectiveness of oral probiotics for the prevention of mastitis in breastfeeding women.MethodsAPProve (CAn Probiotics ImProve Breastfeeding Outcomes?) is a double-blind randomised controlled trial designed to assess outcomes between breastfeeding women ingesting a probiotic versus a placebo daily for 8 weeks following birth. A total of 600 women (300 to each arm) who intend to breastfeed will be randomised after the birth of a term, healthy infant. Daily and weekly surveys for 8 weeks and follow-up surveys at 2, 6 and 12 months after birth will assess the primary outcome of mastitis in the first 8 weeks following birth as well as secondary maternal outcomes of breastfeeding duration (total/partial), antibiotic use, maternal health and well-being, and treatment compliance; and infant outcomes including gastroenteritis, infant health and well-being and growth and development. The acceptability and compliance using a novel mobile phone application system will also be evaluated.DiscussionThere is an urgent need to explore safe and effective alternatives for preventing mastitis in breastfeeding women. This trial seeks to provide evidence for such an alternative in the form of probiotics, which may also increase breastfeeding duration, providing long-term health, cognitive and developmental benefits for children. Decreased antibiotic usage also benefits the community and health system.Trial registrationAustralian New Zealand Clinical Trials Registry: ACTRN12615000923561.Date of registration: 4th September, 2015, retrospectively registered.Electronic supplementary materialThe online version of this article (doi:10.1186/s12884-017-1330-8) contains supplementary material, which is available to authorized users.