Diarrhea is one of leading causes of death in children under five years old. The increasing death rate of children under five has urged people to make efforts in order to decrease the children’s mortality and morbidity rate. In 2016, the case fatality rate (CFR) of diarrhea in Indonesia was increasing from 2.47% to 3.04%. In dealing with diarrhea in children under five, the role of a mother is undoubtedly crucial. The objective of this research was to investigate the correlation between mothers’ knowledge of childhood diarrhea and early management of acute diarrhea in children under five in the working area of Kuta Baro Public Health Service, Aceh Besar Regency. This descriptive-correlational study was conducted with a cross-sectional study approach. The population of this research were 384 mothers of children under five living in five areas in Kuta Baro Sub-District. A number of  86 mothers of children aged 2 to 5 years were chosen as the research samples by using purposive sampling technique. The results analysis showed that there was a correlation between the mothers’ knowledge and the early management of acute diarrhea in children under five (p-value = 0.005), the intake of oralite (p-value = 0.019), and nutrition intake (p-value = 0.000). However, there was no correlation between the mothers’ knowledge and zink intake (p-value = 0.089). Therefore, maintaining health promotion related to early management of acute diarrhea, especially the importance of zink is suggested.