Introduction: The COVID-19 pandemic has imposed an extraordinary challenge to the health and socio-economic facet of nations globally. Health facilities have encountered tremendous challenges to contain service delivery at all levels. This study aims to assess the trend of health service utilization and challenges faced during the COVID-19 pandemic at primary units in Addis Ababa, Ethiopia. Method: A multi-facility-based cross-sectional study was conducted in Addis Ababa between 1 and 30 of August 2020. A mixed-methods design was employed, and both quantitative and qualitative data were collected at 5 health centers. Facilities were selected randomly from 5 sub-cities while interviewees were recruited purposively. A structured questionnaire was used to collect quantitative data from the HMIS units of each facility. Qualitative data was collected using a semi-structured key-informant interview guide. Quantitative data were analyzed using Microsoft Excel, and a 10-month time-series trend was generated. For the qualitative data, qualitative data analysis (QDA-minor) software was used. Results: Time-series comparison of the pre-COVID-19 era loads with the COVID-19 period showed that there was an extensive disparity in the service delivery capacity of the health facilities. A huge drop in inpatient flow of some units such as PICT, VCT, FP services, and most sub-units of the OPDs has been recorded following the COVID-19 outbreak. The key-informant interview also revealed that such challenges, as fear of infection and stigma, poor infrastructure, challenges related to human resources, and challenges related to the supply of prevention and treatment inputs were prominently encountered at the health centers. Conclusion: The COVID-19 wave has negatively impacted many service delivery points in the study settings. The presence of weak infrastructure, lack of PPEs, fear of the infection and stigma, and staff workload have been mentioned as the predominant challenges faced during the outbreak. Health authorities should arrange multifaceted supports to ensure uninterrupted service delivery at primary healthcare units.