Diarrhea is one of the top five causes of death among infants and under-five children in India (1) , despite the availability of easily implementable interventions and existence of National Guidelines for management at the community level. Oral rehydration therapy (ORT) with oral rehydration salt (ORS) solution remains the cornerstone of appropriate case management of diarrheal dehydration and is considered the single most effective strategy toprevent diarrheal deaths in children. Diarrheal illnesses are the leading causes of childhood deaths beyond infancy; it is responsible for 24% of the deaths in children aged 1-4 years, and 17% of all deaths in children 5-14 years. (1). Diarrhea is a common disease and is one of the major determinants of death in pediatric population of the developing Countries.Diarrhea is mainly develop by the lack of healthy practices such as improper breast feeding, unhygienic weaning practices unsafe drinking water, poor practice of hand washing and malnutrition. The mother of rural community areas are unaware about causes sign and symptoms of diarrhea and use of oral rehydration therapy for management of diarrhea. (2) In this context, it was attempted to assess the effectiveness of a structured teaching programme on knowledge regarding the oral rehydration therapy in management of diarrhea among mothers of under five children. A quasi experimental approach with purposive sampling technique was used in the study. The findings of the study shows that the difference between pre-testmean knowledge score of control and experimental group was statistically non-significant at p< 0.05 level whereas the difference between post-test mean knowledge score of both groups was statistically highly significant at p< 0.001 level. It was thus concluded that the structured teaching programme was effective in raising the knowledge level of mothers of under five children regarding the oral rehydration therapy in management of diarrheaand there was statistically significant effect of age, educational status and occupation on knowledge level of mothers of under five children regarding the oral rehydration therapy in management of diarrhea.