Aims: Diarrhoea is a leading cause of mortality and morbidity among children under the age of five years. This study assessed diarrhea treatment behaviour among mothers of under-five attending Ibadan north local government Primary Health Care clinic, Oyo state. Study Design: The survey design was adopted for the study. Primary data was collected from the participants. Place and Duration of Study: The study was conducted in Ibadan north local government Primary Health Care clinic, Oyo state, Nigeria in 2015. Methodology: A structured questionnaire was used to gather data from 370 women randomly selected for the study. Data gathered included socio-demographic, knowledge, treatment behavior, home preparation and use of oral rehydration solution (ORS). Analysis of data was done using descriptive statistics and results presented in frequency tables. The statistical package for social sciences (SPSS version 17) was used for all analyses. Results: Results obtained from the study showed that the majority of the women were traders (35%), Christians (54%), between the ages of 20 and 30 (61%), married (67%) with children below 3 years of age (54%) and indicated that they have had previous births (51%). Most of the respondents had up to secondary education (75%) and indicated that they experience diarrhoea episodes with their children frequently (55%). almost all the women (98%) have heard of diarrhoea and the major source of information was the health workers. Knowledge analysis showed that the respondents have inadequate knowledge regarding causes and prevention measures for diarrhoea. However, 87% of the mothers knew that watery stool is a sign of diarrhea in children and 62% agreed that they gave their children ORS to drink each time they have episodes of diarrhoea. The most common treatment behaviour among the respondents (92% of respondents) was seeking medical attention from hospital during persistent diarrhoeal episode. Further results showed that respondents have inadequate knowledge of preparation and administration of ORS. Conclusion: In conclusion this research showed that there is still a knowledge gap as regards preventive healthcare behaviour in the study area. The need for corroborative post-natal child healthcare education to strengthen the efforts of the healthcare service providers in fighting diarrhoea is thus recommended.