The goal of this paper is to explain the effects of ethanol addition on n-heptane decomposition and partial oxidation processes. An experimental study of the oxidation of n-heptane in the absence and presence of ethanol has been performed. The specific flames were low-pressure (25 Torr), laminar, premixed flames at an equivalence ratio of 1.0. The experiment was performed with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry. Major species on the centerline of each flame were identified by measurements of the photoionization mass spectrum and photoionization efficiency (PIE) spectra. Mole fraction profiles of these species were derived at the selected photon energies near the ionization thresholds. With the addition of ethanol, the partial oxidation of n-heptane into ketones was enhanced and 1-butene mainly decomposed to 1,3-butadiyne instead of 1,3-butadiene. Propargyl radicals were more important than butenynyl and butadienyl radicals in benzene formation.