ObjectiveTo analyze the significance of time to positivity（TTP） of blood culture in differentiating bloodstream infection(BSI) from contamination during blood withdrawal.MethodsClinical data and TTP of blood culture in patients hospitalized in different departments from November 2013 to November 2014 were compared retrospectively, role of TTP in differential diagnosis of BSI was evaluated.ResultsOf 2 605 blood culture specimens, 137 were positive for blood culture，78(56.93%) of which were pathogenic bacteria and 59(43.07%) were contaminated bacteria, coagulase negative staphylococcus had the highest contamination rate（75.76%），while Escherichia coli had the lowest contamination rate（12.50%）. TTP of pathogenic bacteria was shorter than that of contaminated bacteria (［13.86±8.19］ h vs ［40.72±20.96］h, P＜0.05). Of pathogenic bacteria, Enterococcus had the earliest TTP (［10.20±8.00］h),followed by Escherichia coli（［11.12±3.91］ h）, Staphylococcus aureus（［12.22±5.08］h）, Klebsiella pneumoniae（［14.72±10.45］ h）, the other gramnegative bacteria（［16.11±12.97］ h）,and coagulase negative staphylococci（［16.42±5.74］ h）, fungi had the latest TTP （［29.04±3.67］h ）. TTP of gramnegative bacteria was ≤16.59 h, sensitivity and specificity of BSI were 84.09% and 100.00% respectively; TTP of grampositive bacteria was ≤20.96 h, sensitivity and specificity of BSI were 96.77% and 94.44% respectively.ConclusionCombination of TTP of blood culture and other clinical indications can provide reference for early differentiating isolated pathogenic bacteria from contaminated bacteria.