Background: Diarrhea of children under 5 in Malawi, a high-burden country for diarrhea, accounted for 7% of under-5 mortality in 2017. Preceding studies have revealed the association between diarrhea of under-fives and characteristics of children and households including water, sanitation and hygiene (WASH). There has been limited household-level analysis regarding diarrhea in Malawi, thus the aim of our study is to identify risk factors of diarrheal disease among children under 5 in Malawi. Methods: Data set for this study were drawn from the Malawi Demographic and Health Survey conducted in 2015-2016 and 14,872 children were selected as study samples. Independent variables included social-demographic characteristics, household living conditions and WASH environment. Variables that had a P-value lower than 0.05 in the simple logistic analysis were included in multiple logistic regression model. Results: Approximately 20% of children had diarrhea within 2 weeks. In multiple model, demographic characteristics of sex and age of child, size of child at birth, region, mother's age and working status were associated with the risk of diarrhea. Regarding WASH environment, 30 minutes or longer to get water (adjusted odds ratio [AOR], 1.184; 95% confidence interval [CI], 1.045-1.342), unimproved toilet facilities (AOR, 1.185; 95% CI, 1.088-1.291), toilet facilities located in yard/plot (AOR, 1.344; 95% CI, 1.056-1.711) and elsewhere (AOR, 1.375; 95% CI, 1.048-1.805), and lack of handwashing facility with water and soap (AOR, 1.180; 95% CI, 1.010-1.379) increased the odds of diarrhea. Conclusion: The findings of this study showed that socio-demographic characteristics and poor conditions of WASH increased the diarrheal risk of young children. The location of toilet facility implies that proximity is important, but it is necessary to determine the location according to local circumstances. Our study suggests that WASH infrastructure and behavior change strategies need to prioritize Malawi's vulnerable groups.