The crystal structure of rubidium hydrogen carbonate has been determined by single crystal X-ray diffraction method. the crystals are monoclinic with a = 15.05 $AA$, b = 5.83 $AA$, c = 4.02 $AA$, and $eta$ = $107^{circ}.$ There are four chemical units per unit cell and the space-group was fixed as $C2-C^3_2$. Patterson and trial-and-error methods gave the approximate structure and its refinements were made by two-dimentional Fourier summation. The Co3 group is planar with tshhe C-O distances of 1.32 $AA$, 1.32 $AA$, and 1.33 $AA$ within experimental error and the two $CO_3$ groups are linked together to form a complex anion [$H_2C_2O_6$] with the O-H${cdot}{cdot}{cdot}$O distance, 2.53 $AA.$ Two molecules of $RbHCO_3$ make the dimer structure with two hydrogen bonds. The values of reliability factor for $F_{(hol)}$, $F_{(hko)}$and $F_{(okl)}$are 0.15, 0.15 and 0.17 respectively. Each rubidium ion has eight oxygen neighbours with the Rb-O distances of 2.84~3.11 $AA.$