BACKGROUND: There is a large disparity between alcohol treatment access and prevalence of hazardous drinking among same-sex attracted women (SSAW). Yet, this population typically report low satisfaction with care and a reluctance to attend mainstream health services. Currently, there are few culturally tailored services for SSAW available despite evidence indicating that many feel uncomfortable in mainstream services. This paper describes the protocol of a randomised controlled trial aimed at examining the impact of a culturally sensitive four-week short message service (SMS) alcohol intervention on SSAW's alcohol intake, wellbeing, and engagement with alcohol treatment. METHODS: A randomised controlled trial comparing a culturally tailored SMS intervention (The Step One Program) with a generic 'thank you' message, and a nested qualitative study to further explore the intervention's feasibility and acceptability. The Step One Program was co-designed using an Intervention Mapping framework and engaging potential consumers in the developmental process. Participants are block randomised (1:1 ratio) and followed up at the completion of the intervention and at 12 weeks post-intervention. The primary outcomes are alcohol reduction (as measured by the Alcohol Use Disorders Identification Test and self-reported alcohol intake), wellbeing (as measured by the Personal Wellbeing Index - Adult), and help-seeking (as measured by the number of alcohol services accessed and frequency of access). Upon completion of the 12-week post-intervention survey, participants in the intervention group were contacted via email regarding a phone interview on intervention acceptability. DISCUSSION: This study may have important implications for clinical practice, improve healthcare access and equity for SSAW, and provide direction for future research in this field. The outcomes of the current study may stimulate the development of other culturally tailored health programs for SSAW. The results will inform whether individually tailoring the messages according to content and delivery frequency may be warranted to increase its acceptability. TRIAL REGISTRATION: This trial was registered with the Australian New Zealand Clinical Trials Registry (trial ID: ACTRN12617000768392 ).