Background: Pulmonary manifestations as a potential consequence of extraesophageal GERD symptoms have long been hypothesized. Microaspiration of gastric acid into the respiratory tract and lung parenchyma can cause chronic inflammation or trigger exacerbations, while the vagally mediated esophageal-bronchial reflex plays a role in causing or exacerbating bronchoconstriction. This repeated and chronic condition can lead to a decline in lung function. This study aims to determine the association between GERD and lung function parameters. Methods: This research is an analytical observational study with a cross-sectional design, involving spirometry and endoscopic examinations on patients diagnosed with GERD at Dr. Wahidin Sudirohusodo Hospital from June 2024 to September 2024. Lung function parameters were assessed using spirometry, while GERD was examined using EGD. Data were analyzed using the Kolmogorov-smirnov test, chi-square test, and Mann-Whitney test. Results: A total of 100 patients with a normal chest X-ray and symptoms of GERD were included in the study, the majority of whom were under 60 years of age (87%) and female (55%). The mean values of VC, FEV1, and FVC were significantly lower in GERD patients compared to those without GERD (p < 0.005). In GERD patients, restriction abnormalities were more common than normal, with 26 (52%) versus 24 (45%). On the other hand, in patients without GERD, restriction abnormalities were less common than normal, with 16 (32%) versus 34 (68%), and this difference was statistically significant (p = 0.043). The Odds Ratio (OR) was calculated to be 2.302.