Serrated lesions have been considered as benign lesions in the past, but recent studies over the past decade have shown that they have malignant potential. The serrated pathway becomes a new cancerous pathway of colorectal cancer besides conventional adenoma-carcinoma model, inflammation-dysplasia-carcinogenesis and de novo cancer pathways. According to the latest WHO classification criteria, serrated lesions are classified into three types: hyperplastic polyps (HP), sessile serrated lesions (SSL), and traditional serrated adenomas (TSA). Because serrated lesions have relatively specific cancerous pathways and endoscopic characteristics, this article reviews the mechanism of malignant transformation and endoscopic diagnosis and treatment