The thermal decomposition of C2H5OH highly diluted in Ar (1 and 3 ppm) has been studied by monitoring H atoms using the atomic resonance absorption spectrometry (ARAS) technique behind reflected shock waves over the temperature range 1450-1760 K at fixed pressure: 1, 1.45, and 2 atm. The rate constant and the product branching fractions have been determined by analyzing temporal profiles of H atoms; the effect of the secondary reactions on the results has been examined by using a detailed reaction mechanism composed of 103 elementary reactions. The apparent rate constant of ethanol decomposition can be expressed as k1/s-1 = (5.28 ± 0.14) × 1010 exp[-(23530 ± 980)/T] (T = 1450-1670 K, P = 1-2 atm) without a detectable pressure dependence within the tested pressure range of this study. Branching fractions for producing CH3 + CH2OH (1a) and H2O + C2H4 (1b) have been examined by a quantitative measurement of H atoms produced in the successive decompositions of the products CH2OH (1a): the pressure dependence of the branching fraction for channel 1a is obtained by a linear least-squares analysis of the experimental data and can be expressed as φ1a = (0.71 ± 0.07) - (826 ± 116)/T, (0.92 ± 0.04) - (1108 ± 70)/T, and (1.02 ± 0.10) - (1229 ± 168)/T for T = 1450-1760 K, at P = 0.99, 1.45, and 2.0 atm, respectively. The rate constant obtained in this study is found to be consistent with previous theoretical and experimental results; however, the pressure dependence of the branching fraction obtained in this study is smaller than those of previous theoretical works. Modification of the parameters for the decomposition rate in the falloff region is suggested to be important to improve the practical modeling of the pyrolysis and combustion of ethanol.