Objective: To explore the effect of 5-Aza-2′-deoxycytidine (5-Aza-CdR) on the molecular biological behaviors of SW480 cells and the expression of 15-hydroxyprostaglandin dehydrogenase (PGDH). Methods: Colorectal carcinoma SW480 cells were treated with 5-Aza-CdR. Cell proliferation was determined by MTT assay and plate colony formation test. The methylation status of the tumor suppressor gene PGDH was detected by methylation-specific PCR. The expression of PGDH protein was measured by Western blotting and the cell cycle was analyzed by flow cytometry. Results: It was shown that 5-Aza-CdR decreased the proliferation rate of SW480 cells compared with control group. The clony formation rate of SW480 cells decreased significantly after treatment with 5-Aza-CdR in 5 and 10μmol/L compared with the control group (35.4% and 26.5% vs 59.35%, P <0.01). The methylation degree in the promoter of PGDH gene was decreased and the expression of PGDH protein was detected after 5-Aza-CdR treatment. 5-Aza-CdR treatment induced G phase arrest of the SW480 cells. Conclusion: The hypermethylation of CpG islands in the promoter of PGDH gene results in the loss of PGDH protein expression in human colorectal carcinoma cell line. The demethylating agent 5-Aza-CdR could restore PGDH gene expression. These findings provide theoretic evidence for clinical treatment of human colorectal carcinoma with demethylation agent 5-Aza-CdR.