Gastric adenocarcinoma of fundic gland type(GA-FG) with chief cell differentiation was recently proposed as an extremely rare type of gastric adenocarcinoma. Here, we report 4 cases of GA-FG with chief cell differentiation. Endoscopic features included a submucosal tumor shape or a flat shape, whitish discoloration and dilated vessels on the surface. The tumors were located in the upper or middle third of the stomach. All cases were preoperatively diagnosed as GA-FG by biopsy, and endoscopic submucosal dissection was performed. Resected specimens revealed well-differentiated adenocarcinomas resembling chief cells. Tumor cells were diffusely positive for pepsinogen-Ⅰ, but partially positive for H+/K+-ATPase in scattered locations around the tumor margin. Despite the presence of minimal invasion of the carcinoma into the submucosal layer, which was observed in two cases, neither lymphatic nor venous invasion was detected in any of the cases. Finally, all cases showed less aggressive clinical behavior with low grade malignancy. Gastric adenocarcinoma of fundic gland type (GA-FG) with chief cell differentiation was recently proposed as an extremely rare type of gastric adenocarcinoma. Here, we report 4 cases of GA-FG with chief cell differentiation. Endoscopic features included a submucosal tumor shape or a flat shape, whitish discoloration and dilated vessels on the surface. The tumors were located in the upper or middle third of the stomach. All cases were preoperatively diagnosed as GA-FG by biopsy, and endoscopic submucosal dissection was performed. Resected specimens revealed well -differentiated adenocarcinomas resembling chief cells. Tumor cells were diffusely positive for pepsinogen-I, but partially positive for H + / K + -ATPase in scattered locations around the tumor margin. Despite the presence of minimal invasion of the carcinoma into the submucosal layer, which was observed in two cases, neither lymphatic nor venous invasion was detected in any of the cases. Finally, all cases showed less aggressive cl inical behavior with low grade malignancy.