BACKGROUND: Information on health-seeking behavior and utilization of health facilities in slums of Addis Ababa is scarce, impeding the implementation of effective interventions. The purpose of this study is to assess the status of health facilities utilization and predictors for health-seeking behavior of mothers/caregivers of under-five children with acute diarrhea in slums of Addis Ababa, Ethiopia. METHODS: A community-based cross-sectional study design was employed in five rounds of surveys in seven kebeles in slums of Addis Ababa among 472 mothers/caregivers of 472 under-five children with acute diarrhea in reference to Andersen's behavioral model. Data were entered into EpiData Version 3.1 and analyzed using STATA Version 14.0. Descriptive statistics were used to examine patterns of health facilities utilization and multivariable logistic regression analysis was applied to identify predictors associated with health-seeking behavior. RESULTS: Most mothers/caregivers (70.8%) sought care either at home (14.2%) or health facilities (56.6%), whereas 29.2% reported that they did not seek any care. Of those who consulted health facilities, government health facilities (76.9%) were more utilized than private (18.0%) and informal (5.1%) health facilities. Nearly all (93.9%) of the mothers/caregivers using government health facilities used health centers, and of those who took their children to private health facilities (60.9%) used clinics and 26.1% used pharmacies/drug vendors. Mothers/caregivers visiting health facilities obtained mainly oral rehydration salt (ORS) (39.8%) and home-recommended fluids (HRF) (40.3%), but few of them (11.9%) obtained ORS plus zinc supplementation. Predisposing factors of literacy of mothers/caregivers (adjusted odds ratio (AOR) = 2.4; 95% CI 1.4-4.1) and occupation (AOR = 2.6; 95% CI 1.5-4.6), the enabling factors of households monthly income of 50 United States Dollars (US$) and above (AOR = 2.9; 95% CI 1.5-5.6) and availability of nearest health facilities within 15 min walking distance (AOR = 3.3; 95% CI 1.7-6.6), and the need factors of recognizing danger signs of fever (AOR = 4.3; 95% CI 2.4-7.6) and vomiting (AOR = 3.3; 95% CI 1.8-5.9) were significantly associated with health-seeking behavior. CONCLUSIONS: Increasing the proximity of health facilities in slums and health education and socioeconomic development programs targeting illiterate mothers/caregivers and poor households may promote and increase health-seeking behavior and the accessibility of health facilities for the treatment of acute diarrhea in under-five children in Addis Ababa slums.