Abstract: Formaldehyde is a animal carcinogen substance with no adequate evidence in human beings. A retrospective cohort study with using 5875 persons from 4 factories was applied to investigate the relationship between exposing to formaldehyde and cancer death. It showed that the cancer mortality rate in the exposed group (251. 97 per hundred thousand)was significant higher than that in the unexposed group(137.76 per hundred thousand) P<0.001, relative risk (RR) was 1.83. After adjusting sex. age. smoking. alcohol drinking etc. by poisson regression, there was also a significant difference between the two groups P< 0.001, RR was 2. 08, 95% confident interval was 1.51-2.87. So it concluded that exposing to formaldehyde may be a risk factor of cancer death.