BACKGROUND: Data in Ethiopia on the epidemiology of Respiratory Syncytial Virus (RSV) and subtypes among influenza-like illness (ILI) and severe acute respiratory infections (SARI) cases is limited. Here, we assessed the epidemiology of RSV and its subtypes among the pediatric and adult ILI /SARI cases in Ethiopia. METHODS: We conducted prospective, multicenter facility-based study from May 2023 to April 2024. Respiratory swab specimens, epidemiological and clinical data were collected from participants of all age groups, and both hospitalized and non-hospitalized individuals who met the World Health Organization (WHO) case definition for ILI/SARI and provided informed consent. Laboratory investigation was performed using reverse transcription polymerase chain reaction (RT-PCR). Data were analyzed using SPSS V29. Descriptive statistics were used to summarize frequencies and ratios, and multivariable logistic regression model was employed to assess factors associated with RSV positivity. RESULTS: In total, 4170 participants were enrolled, the majority (57.9%) of whom were cases from children under five and SARI (76.5%). RSV was detected in 654 cases (15.7%; 95% CI: 14.6-16.8). RSV subtyping was carried out for 475 (72.6%) of 654 RSV positive samples. The finding revealed that both RSV-A and RSV-B subtypes were co-circulating in Ethiopia, with predominance of RSV-B (68.8%). Age group, season and timing of sample collection were factors independently associated with RSV positivity. Accordingly, children aged < 2 years (AOR: 8.20, 95% CI: 3.57-18.81) and 2-4 years (AOR: 5.01, 95% CI: 2.15-11.67), autumn (AOR: 5.89, 95% CI: 3.79-9.17) and winter (AOR: 3.27, 95% CI: 2.07-5.16) seasons, and case whose samples were collected within three days of symptom onset (AOR: 1.76, 95% CI: 1.09-2.84) were significantly associated with RSV positivity. CONCLUSIONS: The study provides evidence of RSV circulation among ILI/SARI cases in Ethiopia. It also revealed that RSV-B was the predominant subtype circulating in the country. The age-specific and temporal patterns of RSV positivity identified in this study contribute to the understanding of RSV and its subtypes epidemiology in Ethiopia. The findings provide valuable evidence to inform implementation of RSV vaccine introduction programs, particularly targeting high-risk populations during periods of peak transmission. Future research focusing on RSV genomic analysis and disease burden is needed to better understand RSV viral evolution, transmission dynamics and public health impacts in Ethiopia.