Background: Egypt had extended program to eradicate childhood diarrhea and its complications. According to the Egyptian family health survey-2021, the prevalence of diarrhea among children under five years is 12% with higher prevalence in mothers with lower educational level. The aim of the study was to evaluate the effect of health education and determine the influencing factors on mothers' knowledge and behavior regarding managing diarrhea. Methods: pretest-posttest intervention study was carried out in the pediatric clinic on 117 mothers who had children under five years. An interviewer-administered questionnaire was used, composed of three parts (sociodemographic, knowledge assessment, and home management behavior parts). Post-test evaluation was carried out three months after health education. Results: There was significant improvement pre- and post-test in adequate knowledge (40.5% and 89.2%, respectively) and good home management behavior (27% and 83.8%, respectively). Multivariate regression analysis showed that young age and lower educational levels were independent predictors of an inadequate total knowledge score. Young age (less than 25 years old), non-working, and being of medium or low social class were independent predictors of an inadequate total home management behavior for diarrheal disease. Relatives and social media were the main sources of mothers' information (87% and 65%, respectively). Conclusions: Health education was associated with a significant improvement in the mothers' total knowledge and home management behavior, which will positively impact the child's health. Being a simple costless source of information, social media can play a major role in educating mothers about home management of childhood diarrhea.