BACKGROUND: Diet is likely related to sleep quality and mental health, especially during lactation. In this study, we aimed to investigate whether adherence to the healthy Mediterranean diet (MD) was correlated with sleep quality and mental health of breastfeeding mothers and their infants. METHODS: This study was performed on 350 breastfeeding mothers. The participants completed the Edinburgh Postnatal Depression Scale (EPDS), Pittsburg Sleep Quality Index (PSQI), Quality-of-Life Questionnaire (QLQ), Spielberger Anxiety Questionnaire (SAQ), and Infant Sleep Questionnaire (ISQ). A reliable and valid food frequency questionnaire (FFQ) to assess dietary data. RESULTS: Mothers with high adherence to a MD style diet had significantly better sleep quality and quality of life than those with less adherence to a MD. Also, higher MD adherence was related to lower their infant's sleep disorders. After adjusting for the mother's age, body mass index (BMI), and energy intake, adherence to the MD style was associated with high mother's Quality-of-Life (QoL) (β = 1.122
95%CI: 1.066-1.182). Also, MD following related with fewer sleep disorders in infants (OR: 0.857
95%CI: 0.752-0.977). CONCLUSIONS: Our findings suggest that consuming a healthy dietary pattern rich in fruits, vegetables, grains, legumes, nuts, and fish is related with a lower risk of sleep problems in mothers and their infants. Dietary interventional or larger prospective investigations are needed.