A carbon-rich solid product has been synthesized by hydrothermal treatment from fructose with HNO3 at temperature of 140°C. The concentration of the precursor was changed in order to investigate how its change influences formation of carbon microspheres. pH value for every sample was the same, i.e. 1. The formation of the carbon rich solid through the hydrothermal carbonization of fructose is the consequence of dehydration reactions. Obtained carbon material is made of spherical micrometer-sized particles with the diameter in the 1-6 µm range, which can be modulated by modifying the concentration of fructose in solution. The best results are obtained with smaller concentrations of fructose. Spherical particles have more regular shape and they are less agglomerated. The structure and surface chemical properties of obtained material were characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectra and elemental analysis.