This study aimed to assess the utility of the Eastern Cooperative Oncology Group (ECOG) performance scale assessments on days 1 and 8 of palliative care, as well as scale change between these assessments, as prognostic tools for patients with terminally ill cancer. A total of 2392 patients with terminally ill cancer who received palliative care between January 2006 and December 2011 at a single medical center were analyzed. Our study showed that the ECOG scale is a useful prognostic tool to predict life expectancy in patients with terminally ill cancer. The ECOG scale assessments at different time points under palliative care were independent predictors for overall survival. The combined ECOG scale assessments on days 1 and 8 predicted survival more precisely than using day 1 ECOG scale assessment alone.