The use of toilet facilities is a major sanitation intervention, as it reduces the spread of diarrheal diseases. In areas where toilets are misused, human excreta may be disposed of in open fields, bushes, and other open places. However, information about the level of utilization of toilet facilities in developing regions of Ethiopia is limited. Therefore, this study aimed to identify open defecation (OD) levels and determinants of OD among household-owned toilets in Gambella town, Ethiopia. A cross-sectional survey was conducted among 561 households in Gambela Town, using systematic random sampling and questionnaires. The level of OD was analyzed using frequency and percentage. The determinants of OD were assessed using binary logistic regression. Variables with a P-value less than .25 in univariable logistic regression were entered into the multivariable logistic regression model, and statistical significance was declared at a P-value less than .05. The model’s fit was tested using Hosmer and Lemeshow’s goodness of fit. The study found that OD was 47.2% [95% CI: 43.2%-51.4%] among those who owned toilet facilities. The determinants of OD were: occupation of household head [AOR: 5.27, 95% CI: 3.08-9.00], toilet facilities lacking a superstructure [AOR: 2.0, 95% CI: 1.16-3.43], toilet facilities lacking doors [AOR: 3.23, 95% CI: 1.97-5.27], large family size [AOR: 2.16, 95% CI: 1.29-3.60], knowledge of the respondents [AOR: 2.40, 95% CI: 1.50-3.99], and respondents with negative attitude [AOR: 1.76, 95% CI: 1.12-2.74]. Therefore, key stakeholders should focus on improving toilet utilization, considering those factors in their interventions.