Objective To investigate the correlation between the neutrophil percentage(NP) and mortality in the very old patients with infection, and evaluate its application value. Methods A total 191very old patients aged at (86.0±2.0) years with infection admitted in our department between January 2013 and June 2017 were recruited in this study. According to whether they died within 30 d, they were divided into dead group (group A, n=120) and survival group (group B, n=71).The relationship of NP>90%,clinical indicators and complications with 30-day mortality rate was analyzed. SPSS statistics 18.0 was used to perform the statistical analysis. Student’s t test or Chi-square test was employed for different data types. Spearman correlation analysis was adopted for single factor correlation, and logistic regression for multivariate correlation analysis. Results There were no significant differences in age, sex, incidence of complications and white blood cell count (WBC) between the 2 groups (P>0.05). The group A had obviously more patients with NP>90%, higher proportion of sepsis, higher levels of high sensitivity C-reactive protein(hs-CRP), blood lactic acid and procalcitonin (PCT), higher scores of acute physiology and chronic health evaluation (APACHE) Ⅱand sequential organ failure assessment (SOFA), and larger ratios of mechanical ventilation and indwelling catheterization when compared with the group B (P<0.05). Spearman univariate correlation analysis found that 30-day mortality rate was positively correlated with NP>90% (r=0.223), APACHEⅡ score (r=0.156), SOFA score (r=0.316), blood lactic acid (r=0.453), hs-CRP (r=0.656), PCT (r=0.121), sepsis (r=0.286), mechanical ventilation (r=0.461),and indwelling catheterization (r=0.112). Multivariate logistic regression analysis showed that NP>90%, blood lactic acid, hs-CRP, PCT and sepsis were independent risk factors for 30-day mortality rate. Conclusion For the very old patients with infection, NP>90% indicates higher 30-day mortality rate. NP>90% is more sensitive to the extent and condition of infection than WBC.