Even though the proper laboratory techniques have been done to avoid blood reactions before transfusion, still there are blood reactions that have been reported and the source of these reactions are unknown .The purpose of this study was to investigate and analyze the prevalence of bacterial contamination in donated blood collected in Eastern zone blood transfusion centre within Dar es Salaam city. The two objectives guided the study: to determine the prevalence of bacterial contamination in donated blood and to describe the Antimicrobial sensitivity pattern of the isolated bacterial pathogens in the donated blood. This research was conducted using cross section survey with 384 respondents calculated using estimation method formulary : N=Z2P (1-P)/e2 Where by: N= Sample size Z=Standard normal deviate corresponding to two sided (1.96) P=Prevalence of bacteria pathogens in donated blood e= margin of error (5%) thus, N=1.962 X 0.5 (1-0.5)/ (0.05)2 =384. A mixed method was adopted. The quantitative and qualitative data were acquired through observation checklist, documentary review and questionnaire methods as to gather information of respondents. The findings reveled that about 2.8% had bacterial contamination, of which 2.3% were gram positive cocci and 0.5% gram positive rods. Again, the bacterial isolates were about 63.6% coagulase negative staphylococci which were identified as staphylococcus epidermidis whereby 18.2% were micro cocci identified as M.luteus and bacilli species identified as Corynebacterium diphtheroids. Again, sensitivity among the organisms varied; as all the 100% of the organisms isolated being sensitive to amikacin. According to these findings the isolates obtained in the donated blood are skin associated organisms and they are considered as contaminants related to procedure during donor bleeding.