BACKGROUND Blood donors are people who give blood for transfusion. Everywhere in the world, transfusion of human blood is a therapeutic procedure, as there is no genuine substitution. If not well screened for transfusion transmitted infections (HIV,HBV,HCV and Syphilis) can cause infections to the recipients, for instance 5-10% of HIV transmission in Africa is as a result of contaminated blood transfusions. Although blood transfusion is safer than ever before through continued improvements in safe donor recruitment, screening of donors, testing of donated blood and appropriate clinical use of blood, but still there is noticeable prevalence of transfusion transmitted infections, for instance in Dar es Salaam prevalence of transfusion transmitted infections in blood samples was found to be 3.8% for HIV, 8.8% for HBV, 1.5% for HCV, and 4.7% for syphilis in 2006. Current there is increased case reports for HBV, HIV, HCV, and Syphilis in blood samples donated by relatives of patients admitted at KCMC. There is no recent data on Prevalence of transfusion transmitted infections (HIV, HBV, HCV and Syphilis) at KCMC. Therefore this study was trying to find out the burden of transfusion transmitted infections (HIV, HBV, HCV, and Syphilis) at KCMC hospital. BROAD OBJECTIVE The objective of the study was to determine current prevalence of blood transfusion transmitted infections (HIV, HBV, HCV and Syphilis) among blood samples donated by relatives of patients admitted at KCMC. METHODOLOGY Hospital based retrospective cross sectional study design was used. Data were collected from serology and blood transfusion sections at KCMC Clinical Laboratory by using data extraction sheet, where by blood samples donated at KCMC from January to June 2016 were recruited. Data were processed and analyzed by using SPSS version 20. xiii RESULTS A total of 1,246 blood samples from January to June 2016 were enrolled in the study, 2.89% of the blood samples were positive for HIV infection , 7.22% of the blood samples were positive for HBV infection, 0.96% of the blood samples were positive for HCV infection, and 2.17% of the blood samples were positive for syphilis infection. CONCLUSION At KCMC the prevalence of HBV (7.22%) is highest among four transfusion transmitted infections; followed by HIV (2.89%), followed by syphilis (2.17%), and then HCV (0.96%) is lowest among four transfusion transmitted infections being studied in this study.