Negative ion chemical ionization mass spectra were examined for C-1-C-6 n-alkyl nitrates. In contrast to peroxyacyl nitrates, NO3- ions were minor fragments. Major fragment ions were found to be NO2-, and [RO -H-2](-), alkoxy counterparts from which two hydrogen atoms were eliminated. Relative intensity of the two fragment ions largely depends on the speciation, and the [RO - H-2](-)/NO2- ratio increases with the increasing carbon number.