Background <p>Postnatal mothers can experience anxiety, stress and difficulty with mother-infant attachment with potential to lead to an anxiety disorder/depression. There has been an increase in interest in non-pharmacological interventions involving music, with limited evidence assessing effectiveness in this population within randomised controlled trials (RCTs). Mamas in Harmony is a novel music/social support intervention. The objective is to assess the feasibility/acceptability of conducting a full RCT to test the effect and cost-effectiveness of Mamas in Harmony compared with usual care.</p> Methods <p>The pilot RCT aims to recruit 60 mother-infant dyads through social media, community organisations and stakeholder networks, randomly allocated on a 2:1 ratio to the intervention and control group. The intervention group will receive eight 1&#xa0;h weekly Mamas in Harmony sessions plus usual care, and the control group will receive usual care only. Feasibility measures include recruitment, retention and attendance at intervention sessions. The process evaluation aims to establish acceptability of the intervention involving survey evaluation and semi-structured interviews. A priori guidelines have been agreed to establish criteria for progression to a definitive RCT.</p> Discussion <p>The current evidence supports the use of music in reducing anxiety and stress with the recommendation for inclusion of social support. This study has potential to provide robust evidence of the feasibility and acceptability of a music and social support mother-infant group intervention in preparation for a future definitive trial, should progression criteria be met.</p> Trial registration <p>ClinicalTrials.gov ID: <a href="https://classic.clinicaltrials.gov/ct2/show/NCT05930990?term=music+and+social+support&amp;draw=2&amp;rank=1">NCT05930990</a>, registered retrospectively on 5 July 2023. Recruitment commenced on 16 March 2023.</p> Protocol version <p>30 October 2023 Vn 1.0</p>