Near-infrared and visible absorption spectra are measured for nano-energetic materials consisting of thirteen different types of Al or B nano-particles in the 30 nm to 1 mu m size range embedded in nitrocellulose or Teflon oxidizers, using an integrating sphere absorption spectrometer. The Al nano-particle absorption is generally similar to the spectra of bulk Al, but the absorption strength is size-dependent and up to twelve times more intense. Absorption coefficients are determined as a function of nano-particle loading. For Al particles where the size is known, per particle cross sections are also determined. The ratio of cross section to volume decreases with increasing particle size. The implications of these measurements for nano-sized energetic material analysis and for laser-ignition experiments are briefly discussed.