The thermal decomposition of gaseous Et nitrate (I) was studied at 161 deg, 181 deg, and 201 deg C. The data (pressure of the particular component/initial pressure of I) were plotted according to a first-order reaction. The results at 161 deg and 181 deg C were divisible into 2 parts, an initial linear portion and a second linear portion of higher slope; the change in slope occurred at about 50 and 201 deg C did not permit division. The effects of NO sub-2, Et nitrite (II), and Hg on the decomposition rate are discussed. The NO sub-2 content usually did not exceed 10% of the initial amount of I; the NO sub- 2 pressure variation was attributed to NO sub-2 formation from the decomposition of I and NO sub-2 consumption by EtOH, a dissociation product of II. No formed directly from the decomposition of II. The presence of Me nitrite and MeNO sub-2 was established at the end of the reaction. Peak pressures of II occurred at 70 and 62% of the initial concentration of I at 161 deg and 181 deg C, respectively; more II was formed than could be accounted for by the NO sub-2-EtOH reaction. The decompostion mechanism of I cannot be completely explained by attributing the point of molecule fracture of the O-N bond.