ABSTRACT: BACKGROUND:Blood transfusion is a therapeutic procedure that has proven to be effective in saving millions of lives. However, its safety is still a crucial issue that needs due attention. Unsafe blood transfusion is one of the sources of transmission for infectious agents. Therefore, the objective of this study was to assess the sero-prevalence of Transfusion Transmittable Infections (TTIs) such as Human immunodeficiency virus (HIV), Hepatitis B Virus (HBV), Hepatitis C virus (HCV), Treponema pallidum, and associated factors among blood donors in Ethiopia. METHODS:A retrospective cross-sectional study design was used to measure the prevalence of transfusion transmittable infections using data collected from 2014 to 2019 in fourteen blood bank facilities in Ethiopia. Screening of HIV, HBV and HCV was done by using the Enzyme-Linked Immunosorbent Assay (ELISA). Presence of Treponema pallidum infection was assessed using rapid plasma reagin (RPR). Records of blood donors were collected using a checklist from Central Blood Bank Laboratory (BBL) electronic database and reviewed. Data was entered, cleaned and analyzed using SPSS version 23. Logistic regression was fitted to identify factors associated with cumulative TTIs positivity, and for each of the transfusion transmittable infection. P value < 0.05 was considered statistically significant. RESULT:A total of 554,954 blood donors in the fourteen blood bank facilities from 2014-2019 was included in the study. The overall sero-prevalence of HBV, Treponema pallidum, HIV and HCV, was 2.4%, 0.9%, 0.4% and 0.4% respectively. The prevalence of TTIs was comparatively higher in 2014, 5.70% and lowest in 2019, 3.40%. The odds of screening HBV in blood donors in age group of 35-39 and 40-44 were 1.2 [1.1, 1.3] and 1.3 [1.1, 1.5] respectively. The odds of screening HCV in blood donors in the age group of 25-34, 35-44 and 45-54 were 1.3 [1.1, 1.5], 1.3 [1.1, 1.7] and 1.7 [1.2, 2.2] respectively. The likelihood of having at least one infection among blood donors was 1.2 [1.1, 1.3] times in male blood donors compared to female. The odds of getting at least one TTI and Treponema pallidum in unemployed blood donors were 2.4 [2.0, 2.8] and 8.1 [6.1, 10.7] respectively. The probability of getting those who have at least one TTIs, HBV and Treponema pallidum were higher in blood donors those who live in Semi Urban and Rural parts of the country than those who live in Urban areas. The odds of having at least one TTI, HBV and HCV in blood donors with mobile mode of blood donation were 1.4 [1.3, 1.6], 1.6 [1.4, 1.8], and 1.6 [1.1, 2.2]. CONCLUSION:The current magnitudes of TTIs are lower when compared to other previous studies conducted in Ethiopia. Older age, male, occupation, donations from mobile sites, residents of semi urban and rural settings were found to be strongly associated with sero-positivity of TTIs. Hence, strict donor screening and testing particularly taking the above factors into consideration is strongly recommended.