Abstract : Introduction: Rheumatoid arthritis is a common and systemic disease for unknown reasons. Pulmonary involvement is common in patients with rheumatoid arthritis. Lung ultrasound is a safe, easy, and accessible way to diagnose lung cancer. Therefore, the aim of this study was to investigate the diagnostic accuracy of pulmonary ultrasound (US) to find pulmonary parenchymal involvement in patients in patients with rheumatoid arthritis. Materials and Method: This study was performed cross-sectionally with a descriptive-analytical approach on 123 patients with rheumatoid arthritis. After obtaining written consent, all individuals were undergoing lung ultrasound. The results of ultrasound to determine the diagnostic accuracy of this modality in ILD diagnosis, were compared with the findings of HRCT. In the next step, a checklist also included personal information such as gender, age, smoking and drug history for each patient. The collected data were analyzed after coding and logging into SPSS-21 statistical software and analyzed using appropriate statistical tests. Results: Evidence of ILD in HRCT study was observed in 37 subjects (about 30%). Sensitivity and specificity in ILD diagnosis were 64.8% and 60.47%, respectively. The positive predictive value (PPV), negative predictive value (NPV), positive odds ratio and negative odds ratio were estimated at 41.38%, 80%, 1.64, 0.58, respectively and diagnostic accuracy was 61.79%. Ultrasound sensitivity in both mild and moderate B-Line w