Resistance to chemotherapeutic agents has been considered as a major reason for the high incidence rate of recurrence and metastasis suffered by colorectal cancer (CRC) patients. ATP-binding cassette sub-family G member 2 (ABCG2) is involved in drug resistance. DNA methylation of the ABCG2 promoter site has a significant influence on the regulation of epigenetic gene expression. In the present study, we investigated whether the methylation status of the ABCG2 promoter is related to drug sensitivity in CRC cell lines. In order to examine the ABCG2 expression level and identify the methylation status, RT-PCR, qRT-PCR analysis, MS-PCR and bisulfite sequencing were conducted on 32 CRC cell lines. SNU-C4, LS174T and NCI-H716 were selected as low ABCG2-expressing and high promoter methylated cell lines. The cell proliferation assay for 5-fluorouracil, oxaliplatin and irinotecan was performed after 5-aza-2'-deoxycytidine (5-aza) treatment in these cell lines. In the 32 CRC cell lines, 25% of the cell lines expressed low or no ABCG2 expression. Of these cell lines, SNU-C4, LS174T and NCI-H716 were hypermethylated at the promoter region, ~20%. Demethylation of ABCG2 was induced by 5-aza, which enhanced the ABCG2 expression level and influenced the cell proliferation similar to treatment with the anticancer agents. Our data suggest that the ABCG2 expression level regulated by methylation is related to anticancer drug sensitivity. Based on these results, it can be applied to predict the anticancer drug response.