BackgroundIt is important to offer high-quality HIV/AIDS treatment and antiretroviral medication to people living with the disease to improve health outcomes. The quality of health services has become a public health issue.ObjectiveTo assess ART service quality and associated factors at a selected public hospital, Addis Ababa, Ethiopia, in 2021.MethodsA mixed study design was used from April to May 2021. Donabedian’s structure–process–outcome model of health care quality was employed as a framework. A total of 420 clients were interviewed to obtain quantitative data, and 08 key informant interviews and 357 program documents were reviewed. Quantitative data were checked, coded, and entered into Epi Info version 7.2 and exported into SPSS windows version 25.0. In the multivariable logistic regression analysis, variables with p-values < 0.05 and adjusted odds ratio (AOR) with 95% confidence interval (CI) were used to identify factors associated with client satisfaction. Qualitative data were transcribed and analysed using the ATLAS.ti version 8 software program and used to complement the quantitative findings.ResultsThe overall quality of ART services was 73.3% for the availability of resources, 79.5% for healthcare providers’ compliance with the national guidelines, and 86.4% for client satisfaction with the quality of ART clinical services. Patients who disclosed their HIV status [AOR 10.7, 95% CI: 5.2–22], months of ART [AOR 10.4, 95% CI: 3.89–27.8], age group 34–44, 45–55, and 56–76 years were found to be 5.1, 8.1, and 5 [AOR 5.1,95% CI:1.2–22, AOR 8.1,95% CI:1.9–35.5, AOR 5,95% CI:2.97–9.44], respectively, and consultation time [AOR 3.5, 95% CI: 1.6–7.35] were associated with client satisfaction on the quality of ART clinical services.ConclusionThis study revealed that the overall quality of ART services in selected Addis Ababa public hospitals was good, although with the availability of resources and compliance health care providers need improvement.