This dataset contains de-identified data from a before-and-after mixed-methods evaluation of a behavioural science intervention to improve breastfeeding-friendly practices in Kosovo’s primary care system (baseline June–July 2019; endline June–July 2021). The intervention combined Behaviour Centred Design and Human-Centred Design approaches and included activities such as Transformational Forums, Emo-Demo videos, PhotoVoice, posters and brochures, a clinical support app, and advocacy. Data comprise: Provider consultation observations: structured checklist data on breastfeeding-friendly clinical and interpersonal behaviours; Maternal exit interviews (paired with observed consultations): self-reported experience of counselling and breastfeeding-related confidence and intentions. File formats: DTA (data), PDF (survey tools), and DOCX (codebook). All data are anonymised; ethical approvals and informed consent were obtained.