Although the standard treatment for gastric neoplasia is still surgical resection, endoscopic resection has been accepted for some of these lesions in an early stage. Among several methods of endoscopic resection, endoscopic submucosal dissection has been developed to remove the lesions in an en bloc fashion regardless of size, shape, coexisting ulcer, and location. However, indication of endoscopic submucosal dissection is strictly confined by two aspects; those are the possibility of nodal metastases and technical difficulty. Nowadays, several knives for endoscopic submucosal dissection are available and each of them has some merits and demerits. We describe how to perform endoscopic submucosal dissection in the stomach by using the flex-knife, a new endoscopic device specifically designed for submucosal dissection, emphasizing its special features from our experience.