Diarrhoea is widely recognized as a major cause of childhood morbidity and mortality in many developing countries, particularly in sub-Saharan Africa. The objective of this study is to assess the knowledge of causes, management and prevention of diarrhoea among nursing mothers of under-two children in two selected primary health centers in Ibadan North Local Government, Oyo state. A descriptive non-experimental research design was used for the study. One hundred and sixty nursing mothers were selected from the two primary health centers. A structured self-administered questionnaire was used to collect data from participants while descriptive statistics of frequencies and percentages were used to analyze the data on the objectives.The study findings revealed that majority (89.4%) of respondents have heard of diarrhoea before, many of them (45%) had it from health centers and (10.6%) from past experience of diarrhoea occurrence. Majority (78.1%) of respondents had knowledge of diarrhoea, having been able to define what diarrhoea is in their own perspective and were able to identify some causes of diarrhoea. Over half (63.8%) of them claimed their index child had diarrhoea out of which less than half (38.8%) of them managed it with ORS. Less than half of them (34.4%) managed the occurrence at home while (25.5%) took their children to health center. In conclusion, mothers had knowledge of diarrhoea, but knowledge translation to prevention action was very poor. It is recommended that, health education of mothers on prevention should be intensified while mass media should assist in disseminating health information on diarrhoea prevention. Government should provide vaccine against rotavirus which should be included in the routine immunization schedule.