An endoscopic mucosal resection (EMR) is used widely as an alternative treatment to a surgical resection for early gastric neoplastic lesions. Among the unusual complications of gastric EMR, perforation is usually manifested as a pneumoperitoneum. This paper reports a patient with a left-side pneumothorax without pneumoperitoneum as a complication of gastric EMR. The patient developed a left side pneumothorax after gastric EMR in the gastric fundus and recovered without further complications after conservative treatment, including endoscopic clipping.