An experimental study was reported on premixed ethanol/n-heptane/oxygen/argon flames at low pressure (4.655kPa) with ethanol blending ratios of 0 (Flame 1), 15% (Flame 2), and 30% (Flame 3). The equivalence ratio was 1.0. Flame species were identified using molecular beam mass spectrometry with tunable synchrotron photoionization. The flame temperature profiles were measured with a Pt-6%Rh/Pt-30%Rh thermocouple. The mole fraction profiles of major and intermediate flame species under different ethanol ratios were analyzed in this article. Experimental results showed that the temperature profiles of measured flames fall almost on a single curve, which means that ethanol had little effect on flame temperature. The peak mole fraction of the main combustion products occurred 2-6mm above the burner. With the increase of ethanol blending ratios, the mole fractions of H-2, CO, and CO2 decreased, the mole fraction of H2O increased, and the mole fractions of intermediate combustion products (C2H2, C2H4, HCHO, C3H3) decreased. During the combustion process, the oxygen atom of ethanol partly replaces the O-2, thus the final mole fraction of O-2 increased with the increase of ethanol ratios.