Small carbon nanocrystal particle (C20, C24, C26) series, synthesized in an ultrahigh molecular weight polyethylene target by C2 + ion beam irradiation, were studied with respect to their micro structures and sequential growth features. As the samples were examined by laser desorption Time-of-flight mass spectroscopy, relative intensive peaks in the spectrum indicated the presence of C20, C24, C26 carbon clusters. High resolution transmission electron microscopy images and electron diffraction patterns showed that the C20, C24 and C26 assembled into nanocrystal particles. Raman scattering spectrum and Fourier transform infrared spectrum analyses also indicated that the active bonds of small carbon cages were hydrogenated, thus the C20, C24, C26 nanocrystal were formed. Additionally, the sequential growth of C20→C22→C24→C26→...with addition of C2 carbon units was found, which provides a novel and efficient approach to synthesize small hydro-fullerenes and their nanocrystal materials.