To determine whether blood concentrations of Bcl-2 during the 1st week of sepsis could help predict mortality. Serum Bcl-2 concentrations were determined at the 1st, 4th and 8th days of sepsis diagnosis. Thirty-day surviving patients (n = 168) showed higher serum Bcl-2 levels at the 1st (p = 0.002), 4th (p < 0.001) and 8th days (p < 0.001) of sepsis diagnosis than non-surviving patients (n = 91). An association between serum Bcl-2 concentrations at the 1st (p = 0.003), 4th (p < 0.001) and 8th days (p = 0.01) and 30-day mortality after controlling for diabetes mellitus, Sepsis-related Organ Failure Assessment, lactic acid and age was found in the multiple logistic regression analysis. The novel finding is that blood Bcl-2 concentrations at any time in the 1st week of sepsis are associated with mortality.