Natural graphite was chemically modified by an acid mixture (H2SO4/HNO3, 4:1) using sonication. The resulting material was then expanded with octadecylamine by the dispersion method. The sample was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG), wide-angle X-ray diffraction (WAXD) and relaxometry—low-field nuclear magnetic resonance (LFNMR). The SEM images revealed the expansion of the graphite layers. The presence of CH absorption was detected in the infrared spectrum of the expanded sample. The WAXD showed an additional diffraction peak at lower 2θ angle, indicating that intercalation of octadecylamine was successful. The thermogravimetry curve revealed three degradation steps. Two of them could be attributed to different structures (delaminated and exfoliated). The relaxometry showed that the relaxation time was dependon the frequency and the curve of the graphite/octadecylamine presented two peaks—approximately before 106 Hz and after 107 Hz. The results permitted inferring that organically modified graphite was achieved.