The catalytic effect of iron (III) oxide (Fe2O3) and copper (II) oxide (CuO) on an ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB) propellant was studied. High speed (5 kHz) planar laser induced fluorescence (PLIF) and visible microscopic imaging of the surface was carried out in an effort to determine the mechanisms that account for the effect of catalysts. Diffusion flame lengths, crystal burn times, and ignition delay times for single AP crystals were measured during deflagration of catalyzed propellants at 1 atm. A long distance microscopic lens was also used to image AP crystal behavior in the presence of the catalysts. General trends observed on the surface are discussed. The addition of a transition metal oxide (TMO) catalyst greatly reduces the ignition delay times of the AP crystals while not significantly altering the coarse AP crystal burn times. The diffusion flame length was found to increase proportionally with the propellant's burning rate. The findings of this experimental study provide evidence that the fine AP/binder mixture is affected most by the catalyst rather than the coarse AP at 1 atm. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.