BACKGROUND Serrated polyposis syndrome (SPS) is characterized by numerous hyperplastic polyps and sessile serrated adenoma/polyp (SSA/P) in the large intestine. SSA/P is known to transform into malignant lesions through the serrated pathway instead of the adenoma-carcinoma sequence. Early diagnosis with lower gastrointestinal endoscopy and early treatment are now considered to be essential. CASE REPORT We had an experience with a case of SPS to which endoscopic treatment was applied in multiple sessions. Endoscopic treatment was performed for 16 lesions in total, and the pathological findings were SSA/P for 15 and adenoma for the other lesion. We intend to continue performing endoscopic surveillance for any newly developing lesions. CONCLUSIONS SPS has a potential for malignant transformation, and issues, such as long-term prognosis and optimal therapeutic strategies, await resolution. However, multiple endoscopic treatments are useful for cases with lesions that are controllable employing this modality.