Background Previous studies suggest clinical effectiveness of endoscopic full-thickness plication in selected patients with gastroesophageal reflux disease (GERD). The aim of this study was to assess the clinical safety and efficiency of the GERDx™ device by evaluating clinical parameters, reflux symptom scores, and quality of life (QoL). Methods Prospective one-arm trial evaluating the outcome of forty patients with GERD subjected to endoscopic plication with the GERDx™ device. We included patients with at least one typical reflux symptom despite treatment with a PPI for > 6 months, pathologic esophageal acid exposure, hiatal hernia of size < 2 cm, and endoscopic Hill grade II–III. Evaluation of Gastrointestinal Quality of Life Index (GIQLI), symptom scores, esophageal manometry, and impedance-pH-monitoring were performed at baseline and at 3 months after surgery. (Trial Registration: ClinicalTrials.gov NCT 01798212.) Results There were no intraoperative complications. Four out of forty patients experienced postoperative complications requiring intervention. Seven of forty patients were subjected to laparoscopic fundoplication 3 months after endoscopic plication due to persistent symptoms and were lost to further follow-up. Thirty out of forty patients were available at 3-month follow-up. There was an improvement of the GIQLI score, from a mean of 92.45 ± 18.47 to 112.03 ± 13.11 ( p  < 0.001). The general reflux-specific score increased from a mean of 49.84 ± 24.83 to 23.93 ± 15.63 ( p  < 0.001), and the DeMeester score from a mean of 46.48 ± 30.83 to 20.03 ± 23.62 ( p  < 0.001). There was no significant change in manometric data after intervention. Three of thirty patients continued daily antireflux medication. Conclusions Endoscopic plication with the GERDx™ device reduced distal acid exposure of the esophagus, reflux-related symptoms, and improved GIQLI scores with minimal side effects in a selected cohort of patients and may be a safe alternative in the treatment of GERD.