The nuclear magnetic resonance of ²³Na (I=³/₂) in an NaMnCl₃ single crystal grown by the Czochralski method has been investigated by employing a Bruker FT NMR spectrometer. From the experimental data, the quadrupole coupling constant e²qQ/h=155+or-2 kHz and asymmetry parameter eta =0 are determined at room temperature. The principal Z axis of the EFG tensor of the ²³Na, the largest component, is parallel to the crystallographic c axis. The temperature dependence of the quadrupole parameters is also investigated in the temperature range of 140-380 K. The quadrupole coupling constant of ²³Na is found to be linearly increasing as the temperature increases.