- Nursing Science Quarterly
- Nursing Times
- Nutrients
- Nutrition
- Nutrition & Metabolism
- Nutrition and Cancer
- Nutrition Clinique et Métabolisme
- Nutrition in Clinical Practice
- Nutrition Journal
- Nutrition, Metabolism and Cardiovascular Diseases
- Nutrition Research
- Nutritional Neuroscience
- OA Biochemistry
- Obesitologia Hungarica
- Obesity and Metabolism
- Obesity Medicine
- Obesity Research
- Obesity Reviews
- Obstetrics & Gynaecology Today
- Obstetrics and Gynaecology Cases - Reviews
- Obstetrics and Gynecology
- Obstetrics and Gynecology Clinics of North America
- Obzory po Kliniceskoj Farmacologii i Lekarstvennoj Terapii : recenziruemyj naucno-prakticeskij žurnal
- Oceanological and Hydrobiological Studies
- Ochrona Pracy
- Ochrona Roślin
- Ochrona Środowiska
- Ochrona Środowiska i Zasobów Naturalnych
- Ochrona Środowiska i Zdrowia Człowieka
- Ocular Immunology and Inflammation
- Odontoiatria
- Ogólnopolski System Ochrony Zdrowia : OSOZ : w trosce o zdrowsze społeczeństwo.
- Okulistyka
- Okulistyka po Dyplomie
- Okulistyka w Praktyce
- Oncogene
- Oncogenesis
- OncoImmunology
- Oncology
- Oncology in Clinical Practice (d. Onkologia w Praktyce Klinicznej)
- Oncology Letters
- Oncology Reports
- Oncology Research and Treatment
- Oncology Reviews
- OncoReview
- Oncotarget
- OncoTargets and Therapy
- One Health
- Onkologia i Radioterapia
- Onkologia Info
- Onkologia po Dyplomie
- Onkologia Polska
- Onkologia w Praktyce Klinicznej
- Onkologia w Praktyce Klinicznej : Edukacja
- Onkologie
- OnkoRoche
- Open Access Macedonian Journal of Medical Sciences
- Open Chemistry
- Open Forum Infectious Diseases
- Open Journal of Obstetrics and Gynecology
- Open Journal of Ophthalmology
- Open Medicine
- Ophthalmic and Physiological Optics
- Ophthalmic Epidemiology
- Ophthalmic Genetics
- Ophthalmic Plastic and Reconstructive Surgery
- Ophthalmic Research
- Ophthalmic Surgery Lasers & Imaging
- Ophthalmic Surgery Lasers & Imaging Retina (d. Ophthalmic Surgery Lasers & Imaging)
- Ophthalmologica