To investigate the substitution effect of the fluorine atom on methyl group, a methyl group of 2-benzylamino-4, 6-dimethyl-1, 3, 5-triazines was replaced with fluoromethyl, difluoromethyl and trifluoromethyl groups and photosynthetic electron transport (PET) inhibitory and herbicidal activities of these (fluorinated methyl)-1, 3, 5-triazine compounds were evaluated. With increasing the number of fluorine atom of fluorinated methyl group, PET inhibitory activity became higher. Furthermore by introduction of a halogen atom to the 4-position of the benzyl group, PET inhibitory activity was much improved compared to the triazines having an un-substituted benzylamino group. The (fluorinated methyl)-1, 3, 5-triazine derivatives with higher PET inhibitory activity showed also stronger herbicidal activity in soil and foliar application tests.