The current study, guided by the cross-sectional survey method, assessed interface design quality, and its predictive ability on E-learners' post-adoption behavior in E-learning course environments. DeLone and McLean's Information Systems Success Model, Khan's E-learning Framework, and Bhattacherjee's Information System Continuance Model formed the current study's theoretical underpinning. Data for the study were collected from 232 E-learners in selected Ugandan higher learning institutions, using a 38-item self-administered questionnaire. Principal Components Analysis produced a four-factor structure of interface design quality that comprised of content interactivity, accessibility design, system navigation, and visual-aesthetics design, which were found to be valid and reliable using Confirmatory Factor Analysis. The Structural Equation Model fit indices revealed that the hypothesised model achieved adequate goodness-of-fit to the data. Regarding the structural relationships, the four factors were found to be statistically significant predictors of E-learners' satisfaction; and in-turn, satisfaction impacted learning agility. The results have clearly aligned with the study's theoretical framework, buttressing existing empirical data on interface designs and end-user post adoption with E-learning interventions. The current study is crucial for making evidence-based pedagogical and design decisions by key E-learning stakeholders for the successful implementation and continued use of digital learning solutions in higher education contexts.