Endoscopic submucosal dissection (ESD) is now accepted as a minimally invasive treatment for early gastric cancer (EGC). To our knowledge, however, the functional effects of ESD have not been determined in patients with EGC. We therefore investigated whether gastric motility was affected by ESD. Using the (13) C-octanoic acid breath test, gastric emptying of solid test meals was examined in 26 EGC patients and 18 healthy controls, with EGC patients assayed before and about 2 months after ESD. Based on (13) CO2 breath-excretion curves, the lag-phase time (T(lag) ), half-emptying time (T(1/2) ), and gastric emptying coefficient (GEC) were calculated as indices of gastric emptying. In healthy controls, the mean T(lag), T(1/2), and GEC were 85.5 ± 4.9 min, 148.5 ± 8.0 min, and 3.01 ± 0.09 h, respectively. Before ESD, the mean T(lag) , T(1/2), and GEC in the EGC patients were 90.1 ± 5.5 min, 174.7 ± 10.4 min, 2.64 ± 0.08 h, respectively. GEC, but not T(lag) or T(1/2), differed significantly in the two groups, with gastric emptying slower in EGC patients than in controls. Relative to before ESD, the mean T(lag), T(1/2), and GEC in EGC patients after ESD were 109.2% ± 7.8%, 107.9% ± 9.6%, 108.4% ± 4.7%, respectively, indicating that ESD did not significantly affect any of these gastric emptying parameters in EGC patients. ESD is an effective treatment for EGC both in preserving organs and gastric motility.