An experimental study of a Monomethylhydrazine (MMH)/nitrogen tetroxide (NTO) counterflow pool flame was conducted to obtain data that contributes to proposed detailed chemical reaction mechanisms. The flames were imaged through high-speed imaging of chemiluminescence of broad band light emission with Band Pass Filters (BPF) centered at 310 nm +/- 5 nm and 430 nm +/- 5 nm. To help explain the flame structures observed in the experiment, one-dimensional numerical simulations with detailed chemical kinetics were also performed, considering, along with the proposed reaction mechanisms, the MMH evaporation environment at the boundary conditions. The experimental results show a multi-layered flame structure of an MMH/NTO non-premixed flame composed of two orange flames and one weak blue/white flame. Results obtained in numerical simulations indicate that MMH/NTO forms the multi-layered flame structures of two orange flames due to NH3 decomposition and NO2 recombination, and the blue/white flame was newly found in the region between the two orange flames. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.