The C-reactive protein (CRP) levels obtained at hospital admission are associated with the prognosis of several cardiovascular diseases, including acute coronary syndrome. Although the admission CRP level is associated with in-hospital mortality in patients with acute decompensated heart failure (ADHF), there are limited data on the association between the admission CRP level and long-term mortality in patients with ADHF. This study included consecutive ADHF patients admitted to our institution from 2007 to 2011. Eligible patients were divided into four groups based on quartiles of admission CRP levels. The association between the admission CRP level and long-term mortality was assessed by multivariable Cox proportional analysis, including other independent variables with p values < 0.1 in the univariable analyses. Overall, 527 eligible patients were examined. There were 142 deaths (27%) during a median follow-up period of 2.0 years. In the multivariable analysis, the hazard ratio (HR) significantly increased with admission CRP levels in a dose-dependent manner for mortality (p for trend = 0.034). Multivariable analysis also showed a significant association between the admission CRP level, when treated as a natural logarithm-transformed continuous variable, and increased mortality (HR 1.16, p = 0.030). In patients with ADHF, the admission CRP level was associated with an increased risk of long-term mortality.