Many researchers suggested that ultrathin endoscopy improves patient acceptance of endoscopic examinations. However, ultrathin endoscopy provides less image resolution and luminous intensity. Therefore, we focused on the visibility of early gastric cancer on ultrathin endoscopy with Flexible spectral imaging color enhancement (FICE) in this study. Thirty-six patients with early gastric cancer were prospectively enrolled. One endoscopist performed the endoscopic examinations by white light conventional endoscopy (W-CE), white light ultrathin endoscopy (W-UE), FICE ultrathin endoscopy (F-UE) and white light plus FICE ultrathin endoscopy (WF-UE) in the patients. Four other endoscopists were asked to evaluate the visibility of gastric cancer on the W-CE, W-UE, F-UE and WF-UE images with a 5-point Likert scale. The lesions were classified as uncolored, normocolored or reddish. We examined the color difference between early gastric cancer and the surrounding mucosa. To examine the relationship between the color difference and the vessel density, we also measured the difference in vessel density using pathologic specimens stained with hematoxylin and eosin. The Likert score of WF-UE was significantly higher than those of the other three methods (p<0.001). The color difference of F-UE was higher than that of W-CE in the reddish group (p=0.049). The difference in vessel density was higher in the reddish group than in the normocolored group (p=0.048). In conclusion, the visibility of early gastric cancer from the surrounding mucosa using ultrathin endoscopy with FICE was better than that using white light conventional endoscopy, especially for reddish lesions.