Cancer cells acquire metastatic phenotypes by accumulating genetic and epigenetic abnormalities. DNA methylation is involved in epigenetic regulation of gene transcription and frequently altered with carcinogenesis. Two modes of aberrant DNA methylation, promoter hypermethylation and global hypomethylation, play a role in cancer metastasis with different mechanisms. Here, we discuss how the aberrant DNA methylation contributes to acquisition of metastatic phenotypes in cancer and review the recent trials for molecular diagnosis of cancer metastasis using methylation markers.