- Nuclear Science: The study of the metabolic and physiological response of the body to set diet or particular sets of diets.
- Nutrition Science: It is the study of the metabolic and physiological response of the body to set diet or particular sets of diets.
- Obstetrics: It deals with the care of women during pregnancy.
- Oceanography: It is the study of ocean.
- Odontology: The scientific study of the structure and diseases of the teeth.
- Oncology: It is the science that deals with tumors and cancers.
- Oneirology: It is the scientific study of dreams.
- Ophthalmology: This is the study of the structure and diseases related to the eye.
- Organic Chemistry: It deals with the structure, properties and reactions of compounds that contain carbon.
- Ornithology: It is the study of the birds.