To evaluate the clinical significance of SpvO2 and to compare the correlation and agreement between SpvO2 and ScvO2 in severe sepsis or septic shock. It was a prospective observational study in patients who visited ED and diagnosed as severe sepsis or septic shock from Mar. 2009 to Sep. 2012. The outcome was 28-day mortality. The blood sample was obtained at initial and at 6 hr after initial resuscitation. From 380 eligible patients, 241 patients were included. The overall 28-day mortality was 17.0%. Baseline ScvO2 and SpvO2 values were not significantly different between survivors and nonsurvivors. After 6-hr management, SpvO2 were significantly lower in non-survivors than survivors. But, ScvO2 was not significantly different between groups. In survivor group, correlation between ScvO2 and SpvO2 was significant at initial and after 6-hour resuscitation (Spearman r = 0.290, p < 0.001; Spearman r = 0.307, p < 0.001, respectively). However, in non-survivor group, correlation was not significant (Spearman r = 0.172, p=0.315 at baseline; Spearman r = 0.136, p=0.397 at 6-hr resuscitation). Initial lactate values were significantly correlated with SpvO2 at baseline (Spearman r =-0.199, p=0.004) but not with ScvO2 (Spearman r =-0.054, p=0.445). After 6-hr resuscitation, blood lactate values were significantly correlated with SpvO2 but not with ScvO2 (lactate vs SpvO2, Pearson r=-0.437, p< 0.001; lactate vs ScvO2, Pearson r=-0.028, p=0.6934, respectively). Mortality rate was significantly higher in SpvO2 < 70% group than in SpvO2 >70% group without reference to ScvO2 values. And patients who had ScvO2>70% and SpvO2>70% were significantly higher survival times during 28-day follow-up period. Agreement between SpvO2 and ScvO2 was poor and SpvO2 was not correlated with ScvO2 especially in non-survivor group. However, SpvO2 values were significantly correlated with lactate values and the achievement of SpvO2 >70% during initial resuscitation showed significantly lower 28-day mortality without reference to ScvO2.