Background: A quality medical laboratory service is an important part of the health care system.rnCommitment of the health personnel, administration and policy makers contribute to therncontinuous improvement of diagnosis. In developing countries like Ethiopia, the laboratoryrnquality system remains weak due to several factors. Therefore, assessing the factors affectingrnquality of medical laboratory service is highly important in order to improve service quality.rnObjective: To assess factors affecting the quality of medical laboratory service in South WestrnShewa Zone Health Facilities, Oromia, Ethiopia, January 2020 to May 2020.rnMethods: An institution based cross-sectional study was conducted at South West Shewa ZonernHealth Facilities from January 2020 to May 2020. A pretested, structured questionnaire andrnchecklist was used to collect the socio-demographic information of the study participants and tornassess factors affecting the provision of quality medical laboratory services. Data were checkedrnfor completeness, entered, and analyzed using SPSS version 24. The strength of associationrnbetween the dependent and independent variables was assessed using binary and multiple logisticrnregression analysis. A p-value < 0.05 was considered statistically significant.rnResults: A total of 85 medical laboratory professionals participated in the study. Of these, 68rn(80%) were males and 27 (31.8%), were laboratory technologists. Of them 78 (91.8%) were notrnsatisfied with their salary. Thirty-two (37.6%) of the participants reported that their laboratoryrndid not provide quality laboratory service. Lack of Quality Manual, Lack of staff recognition andrnnot conducting Internal Quality control activitieswere the major factors significantly associatedrnwith poor quality laboratory service (p < 0.05).High work load was identified as the highestrntechnical factor influenced the provision of quality laboratory services 56.1%, followed byrnEquipment Failure 20% and from administrative factors shortage of resources was rated highestrn39% followed by poor staff commitment 23.4%.rnConclusions:More thanOne third of the study participants reported that their laboratory did notrnprovide quality laboratory services. Lack of quality manual, not conducting internal qualityrncontrol activities and Lack of staff recognitionare the major factors associated with poor qualityrnof laboratory services. Hence timely intervention of these factors is warranted since a third of thernparticipants believe their laboratory does not provide quality service.