This study is to identify the association of urinary N-methylformamide level (UNMFL) with cancer mortality in N, N-dimethylformamide (DMF)-exposed male workers in Korea. A cohort was composed of 11,953 DMF exposed workers working between January 1, 2000, and December 31, 2004. These cohort members were matched with the mortality data of the Korean National Statistical Office to follow-up for cancer mortality between 2000 and 2011. Standardised Mortality Ratios (SMRs) of DMF exposed workers with reference to Korean men were calculated. Also controlling age, other carcinogen exposure including hepatitis B and C, the Adjusted Hazard Ratios (AHRs) of workers categorised by the 3 groups of UNMFL with reference to workers with zero UNMFL were calculated. There were no significantly increased or decreased SMRs except for stomach cancer (SMR=0.38, 95%CI=0.10–0.98). The AHRs of overall cancer mortality were significantly increased in in workers with 7.5 to 15 mg/L (SMR=2.72, 95% CI=1.09–6.81) and 15 and over 15 mg/L (SMR=2.41, 95% CI=1.03–5.66) compared with workers with 0 UNMFL. Hepatocellular carcinoma mortality (AHR=3.73, 95% CI=1.05–13.24) of workers with 15 and over 15 mg/L and lung cancer mortality (SMR=14.36, 95% CI=1.41–146.86) in workers with 7.5 to 15 mg/L were significantly increased compared with workers with 0 UNMFL. In this study workers with high UNMFL showed increased mortalities for overall, liver and lung cancer comparing to those of workers with zero UNMFL, which suggests DMF might be caused cancer, especially hepatocellular carcinoma which was approved carcinogenicity on liver in animal experiments.