The oral hygiene is not relatively good cause of smoking, ignoring oral hygiene, not having enough self-care skills and independent living in case mental illness. Their grinding the teeth, serotonin decreases when the people are depressed and then it makes the carbohydrates increases, loses the sense of taste. Therefore they use a lot of sweet, the salivary output decreases, increase in the number of lactobacili and then it makes the cause ofabnormal disease detections including tooth decay, trigeminus neural pain in temporomandibular joint /TMJ/, oral yeast infection, oral bad breath, burning sensation of the tongue, chronic facial pain. Also the oral can disease detects from drug causes like using the anti-depression drugs for at least 6 months.Using analytical research permanent design, I got 55 patients to take part in the survey who are staying in 5th flat , National Clinic of Mental Health from 22nd of September 2014 until 26th of September. When I do the research for history of their patients: among the diagnosis of 16 people disorder depressed, the 13 patients agreed to have a preventive examination voluntary, one of them declined to do it. I use many methods of researching like questionnaire methods interview method, prevention oforal cavity and clinical examinations, respectively Study shows that curriculum contents of School of Nursing, Mongolian National University of Medical Sciences have comparatively less contents of understanding about healthy person, assessment on human, giving advice healthy human, path anatomy, physiology, communication skills.The most of the survey participant patients have holes in their teeth, gum inflammation, and tongue stress disorder. It shows that it decreased to pay attention on their oral hygiene associated with symptoms and it effects directly related to the decrease in salivary output.Depressed People are so bad at paying attention to their oral hygiene habits.