Background: Breastfeeding is of great importance for infant health both short and long term, especially for those born preterm. Apart from the socio-economic and cultural factors which may influence a mother's decision on breastfeeding, lactation performance is also influenced by maternal physiological and psychological condition, as well as infant behavioural factors. The aim of this project is to investigate physiological, psychological and anthropological aspects of 'signalling' between mother and infant during lactation in a stressful situation, following late preterm delivery, using an experimental approach. Method: A single blind parallel randomised controlled trial will be conducted in Chinese primiparous mothers who deliver a infant (34 0/7-37 6/7) weeks and plan to exclusively breastfeed. Mothers will be recruited from four local community clinics attached to Beijing Children Hospital. Two home visits will be arranged at one week and eight weeks postpartum. Participants will be randomly assigned to either intervention arm or control (no intervention) before the first home visit. Mothers from the intervention group will be asked to listen to an audio recording with relaxation meditation daily during breastfeeding. Maternal stress and anxiety will be measured at one week and eight week postpartum using Chinese version of Cohen's Perceived Stress Scale (PSS) and Beck Anxiety Inventory (BAI). Infant weight and length gain (as SD scores) from one to eight week will be measured using anthropometry. Milk volume will be measured using 48-h test-weighing method. Breast milk samples and mother and infant's stool samples will be collected to measure macronutrient and microbiome content. Anthropometric measurements (weight, length and head circumference) will be performed during all home visits. Discussion: Primary outcomes of this study will be the effect of the intervention on maternal psychological state, and infant growth. Other outcomes will include the effect of the intervention on milk production, infant behaviours, and the microbiome composition in breastmilk and maternal and infant's gut. Results of this study will provide greater understanding about maternal-infant factors which influence the success of breastfeeding, and which may then be useful targets for future interventions. Trial registration: ClinicalTrials.gov identifier: NCT03674632. Registered 14 September 2018. © 2019 The Author(s).