Obstructive sleep apnea (OSA) leads to upper respiratory tract obstruction, causing increased abdominal-gastric pressure and decreased lower esophageal sphincter (LES) pressure and thus gastroesophageal reflux (GER). Continuous positive airway pressure (CPAP) is known to be an effective method for OSA treatment, but its effect on GER is still controversial. There are a very few studies investigating CPAP and GER relationship and performed based on pre- and post-treatment objective parameters of GER in patients with OSA. The study investigated the effect of CPAP treatment in patients with moderate and severe OSA without GER complaints on pre- and post-treatment objective GER parameters. The study included 25 patients with respiratory disturbance indices > 15 without reflux symptoms who had undergone polysomnography at sleep laboratory. Age, sex, body mass index (BMI), waist, and neck circumference of the patients were documented. DeMeester score, LES pressure, and polysomnography parameters were evaluated pre- and post-CPAP. The results were statistically evaluated, and p value < 0.05 is considered significant. Out of 25 patients, 21 were male (84 %) and mean age was 49.2 +/- 8.6 (range 31-66). At the pre-CPAP phase, mean sphincter pressure was 22.2 +/- 1.2 (range 8-73), and mean DeMeester score was 18 +/- 15.5 (range 0.2-57). At the post-CPAP, mean sphincter pressure was 22.9 +/- 1.6 (range 9-95), and mean DeMeester score was 16.3 +/- 14.8 (range 0.2-55). No significant difference (p > 0.05) was found comparing pre-CPAP and post-CPAP measurements. Objective criteria show that CPAP treatment does not cause reflux in patients with OSA. Unlike studies reported in the literature, this conclusion has been reached by pre- and post-CPAP assessments.