This is a quasi-experimental research, carried out to evaluate the effect of the health education program in order to prevent and control of diarrhea in children under 3 years of age, referring to urban health centers in south of Tehran with their mothers. For this purpose, 90 mothers whose children had diarrhea, were selected randomly and were divided into experimental and control group.The measuring instruments were questionnaire and observational checklist. The data were collected three times before and after educational intervention program (E.P.I). The E.P.I was performed regarding to predisposing, reinforcing and enabling factors and every mother was educated practically and theoretically at least two sessions in her house.Furthermore the normal defecation of children were identified and recorded separatley.In this study, the rate and duration of diarrhea in the children were followed for three months after (E.I.P). The results showed that peiforming the health educational program (HE.P) not only reduce the rate of diarrhea (P=0.01). It can also, reduce the duration of diarrhea significantly in experimental versus comparing with control group (P=0.014).According to our results. we can say that performing a (H.E.P) is an effective approach in prevention of diarrhea in children under three years of age and also educating in house by using health educational model (esp.precede model) is one of the best way in progressing the mothers hygiene behaviors related to nutrition and personal hygiene.