The impulse acoustic microscopy method was applied to observe the bulk microstructure and to measure sonic velocities and elastic moduli in the carbon nanocomposite specimens prepared by a traditional method and with the use of a vacuum mixer. It is shown that carbon nanoparticles tend to cluster and form micron-sized aggregates. The impulse acoustic microscopy technique makes it possible to visualize a non-uniform distribution of carbon nanofillers over the specimen bulk. Both nanotube and nanoplatelets conglomerates are visible most likely due to the air containing. Results of the elastic measurements demonstrate homogeneity of elastic properties over the material bulk and a weak dependence of sonic velocities and elastic moduli on the filler content. Reduction of the air content and enhancement of elastic properties are observed when increasing the nanofiller content and employing the vacuum mixing technology in nanocomposite fabrication. POLYM. ENG. SCI., 57:697-702, 2017. (c) 2017 Society of Plastics Engineers