Background <p>This study aimed to evaluate the associations between neutrophil percentage-to-albumin ratio (NPAR) and both all-cause and cardiovascular mortality in diabetic kidney disease (DKD) patients.</p> Methods <p>The data for this study were sourced from the National Health and Nutrition Examination Survey (NHANES) 1999–2018. Weighted logistic regression, Cox proportional hazards model, and Fine-Gray competing risk model were used to assess the association between NPAR and both all-cause and cardiovascular mortality in DKD patients.</p> Results <p>A total of 2,699 participants were enrolled in this study. Cox regression analysis revealed that elevated NPAR levels were associated with a higher risk of all-cause mortality in all participants (HR: 2.17, 95%CI: 1.83–2.58). Meanwhile, a significant difference in cardiovascular mortality was observed in males (HR: 1.83, 95%CI: 1.42–2.38) but not in females. Finally, the adjusted Fine-Gray model identified NPAR as an independent predictor of cardiovascular mortality in males (SHR: 1.86 95%CI: 1.28–2.72) but not in females.</p> Conclusions <p>In a nationally representative sample of DKD participants in the US, a significant association was detected between elevated NPAR and increased all-cause and cardiovascular mortality. In addition, gender differences in the relationship between NPAR and both all-cause and cardiovascular mortality were also observed.</p>