AbstractA new subtype of serrated lesions, superficially serrated adenoma (SuSA), has been proposed as a lesion that histopathologically exhibits the morphological features of both conventional adenomas and serrated lesions and is difficult to classify as either one. SuSA has been elucidated to be a precursor lesion ofKRAS‐type traditional serrated adenoma. It has also been reported that SuSA may have malignant potential.We report a case treated with endoscopic submucosal dissection and detailed observation. Endoscopy revealed a raised lesion with a two‐tier raised appearance in the sigmoid colon: a tall pinecone‐like reddish structure and flattened whitish elevation on white light imaging. Magnifying narrow‐band imaging revealed conspicuous blood vessels in the pinecone‐like structure and slightly dilated reticular vessels in the flattened area. Crystal violet staining showed that the pinecone‐like structure had a type IVHpit pattern and the flattened area had a stellate to slightly elongated type IIIHpit pattern diagnosed based on Kudo's classification and other pit pattern classification systems. Ki67‐positive cells were distributed in the basal and middle layers of the gland in the flattened elevated area. Genetic analysis results were positive forKRASmutation and negative forBRAFmutation. Histopathological examination revealed a traditional serrated adenoma in the pinecone‐like structure and SuSA in the adjacent flattened elevated area.