Nanographite (NG) particles were produced by annealing of superpurified detonation nanodiamonds (grain size ~ 5 nm) at 1600 °C. The aim of this research was to provide Raman characterization of nanographites obtained and to investigate characteristic features of UV optical absorption in NG suspensions caused by the excitation of surface plasmon resonance (SPR) and its dependence on disorder and defectiveness of graphene shells during their transformation. The 1-st and 2-nd order Raman spectra of the NG samples excited at 514 nm were analyzed. Two different approaches applied for evaluation of the in-plane NG crystallite sizes by using the D- and G-band intensities ratio gave quite different results (~ 3.5 nm and ~ 5.5 nm) reflecting, most likely, a complicated NG structure. The changes in both intensity and position of SPR absorption peak for water suspension of NG particles may originate in structural imperfections and/or changes in aggregation of NG particles.Research Highlights► Nanographite particles are produced by annealing of detonation nanodiamonds. ► Raman spectra of NG have common features with the spectra of disordered graphites. ► The crystalline sizes remain practically the same within the annealing time interval. ► Improvement the structural perfection of nanographites in the course of annealing. ► The shape and position of SPR absorption peak of NG particles in water suspension.