Chronic inflammation is implicated in cancer prognosis and can be modulated by diet. We examined associations between post-diagnosis dietary inflammatory potential and mortality outcomes among post-menopausal women diagnosed with cancer in the Women’s Health Initiative (WHI). Energy-adjusted dietary inflammatory index scores (E-DII) were calculated from dietary and supplemental intake data collected on the first food frequency questionnaire following the diagnosis of primary invasive cancer for 3434 women in the WHI. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CIs) for risk of death from any cause, cancer, cardiovascular disease (CVD) and other causes by post-diagnosis quartiles of E-DII. Subgroup analyses by cancer stage and grade were performed. There were 1156 deaths after a median 13 years of follow-up from the date of a cancer diagnosis. In the multivariable-adjusted analyses, a more anti-inflammatory diet plus supplements after cancer diagnosis was associated with lower all-cause mortality, cancer mortality, CVD mortality and mortality from other causes with HRsQ1vs.Q4 ranging from 0.47 to 0.68 (all P-trends < 0.05). Associations were stronger for cancers diagnosed at more distant stages or moderately differentiated grades. A more anti-inflammatory diet plus supplements after a cancer diagnosis may improve survival for post-menopausal cancer survivors.