Objective: To investigate the diagnostic value of impulse oscillometry (IOS) in older patients with chronic obstructive pulmonary disease (COPD). Methods: This single-center observational study enrolled 670 older patients with COPD and 101 healthy controls who attended the First Affiliated Hospital of Nanjing Medical University between September 2019 and August 2023. All participants underwent IOS followed by spirometry. Demographic characteristics, IOS parameters, and spirometric indices were collected. IOS measurements were performed in strict accordance with international and Chinese guidelines. Respiratory system resistance at 5, 10, and 20 Hz (R5, R10, and R20), respiratory system reactance at 5, 10, and 20 Hz (X5, X10, and X20), the difference between R5 and R20 (R5–R20), and resonant frequency (Fres) were recorded and converted to Z scores. Spearman correlation analysis, generalized linear models with a gamma distribution and log-link function, and median quantile regression (τ = 0.5) were used to evaluate the associations between IOS parameters and spirometric indices. Receiver operating characteristic (ROC) curve analysis was performed to assess diagnostic performance. Results: Compared with healthy controls, patients with COPD had significantly higher R5, R5–R20, and Fres and significantly lower X5 values (all P < 0.001). R5, R5–R20, and Fres were negatively correlated with the percentage of predicted forced expiratory volume in 1 second (FEV?% predicted; R5: r = ?0.500, P < 0.001; R5–R20: r = ?0.584, P < 0.001; Fres: r = ?0.546, P < 0.001). In contrast, X5 and X20 were positively correlated with FEV?% predicted (X5: r = 0.609, P < 0.001; X20: r = 0.529, P < 0.001). After adjustment for age, sex, body mass index, and smoking index, R5–R20 was 34.3%, 119.2%, and 189.2% higher in patients with Global Initiative for Chronic Obstructive Lung Disease (GOLD) grades 2, 3, and 4, respectively, than in those with GOLD grade 1 (all P < 0.001). The corresponding increases in R5 were 15.2%, 49.3%, and 66.6% (all P < 0.001), whereas Fres increased by 16.0%, 42.1%, and 64.6%, respectively (all P < 0.001). X5 and X20 progressively decreased with increasing GOLD grade. The regression coefficients for X5 were ?0.047, ?0.186, and ?0.328 for GOLD grades 2, 3, and 4, respectively, and those for X20 were ?0.025, ?0.059, and ?0.089, respectively (all P < 0.001). A multivariable model combining Fres, R5, R20, X5, and X20 demonstrated improved diagnostic performance, with an area under the ROC curve of 0.803 (95% confidence interval: 0.761–0.845), a sensitivity of 59%, a specificity of 88%, and a Nagelkerke R² of 0.38. Conclusion: IOS can effectively characterize airway resistance and the elastic properties of the respiratory system in older patients with COPD. A diagnostic model combining multiple IOS parameters showed moderate diagnostic performance and may serve as a useful adjunctive tool for the diagnosis of COPD in older adults.