NaMg[$Cr(C_2O_4)_3]{cdot}10H_2O$ crystallizes in the trigonal space group P$ar{3}$c1, with a=b= 16.969(3), c=12.521(3) ${AA}$, ${alpha}={eta}=90^{circ},;{gamma}=120^{circ},;{ ho}=1.734 ;gcm^{-3},;{mu}=6.46;cm^{-1}$, Z=6. Intensities for 1062 unique reflections were measured on a four-circle diffractometer with Mo K${alpha}$ radiation (${lambda}=0.71069;{AA}$). The structure was solved by direct methods and refined to a final ${omega}$R value of 0.084. X-ray crystal structure showed that magnesium ion appears to be occupied over two sites with the occupancy ratio of 2:1. The crystal possesses 10 water molecules instead of previously estimated 9 water molecules.