The present invention relates to the novel use of syndecan-2 (SDC2) gene as a CpG methylation biomarker for detecting precancerous lesions, and more particularly, to the use of the SDC2 gene as a biomarker to early diagnose colorectal precancerous lesions by measuring the degree of methylation of the SDC2 gene. The present invention provides a method of providing information for diagnosis of precancerous lesions by detecting methylation of the CpG islands of the SDC2 gene. In addition, the use of the methylation detection and kit according to the present invention makes it possible to diagnose colorectal precancerous lesions at an early transformation stage, thus enabling the early diagnosis of colorectal precancerous lesions. Furthermore, the methylation detection method and kit of the present invention enables colorectal precancerous lesions to be effectively diagnosed in an accurate and rapid manner compared to conventional methods.