It consists of rubidium cations Rb+ and oxalate anions C2O2−4.

[5] Freshly prepared anhydrous rubidium oxalate initially contains mainly the monoclinic form, but this slowly transforms irreversibly into the orthorhombic form.

[6][2] In addition to the neutral rubidium oxalate Rb2C2O4, there is also an acidic salt, rubidium hydrogen oxalate with the formula RbHC2O4, which is isomorphic to potassium hydrogen oxalate KHC2O4[10] and forms monoclinic crystals,[11] and an acidic dioxalate with the formula RbHC2O4·H2C2O4, which exists as a dihydrate, has a density of 2.125 g/cm3 at 18 °C and a solubility of 21 g/L at 21 °C.

[12] Upon evaporation of a solution in hydrogen peroxide, rubidium oxalate forms a monoperhydrate of the formula Rb2C2O4·H2O2, which forms monoclinic crystals that are relatively stable in air.

[13] Rubidium oxalate reacts with hydrogen fluoride to form a hydrofluoridate salt (RbHC2O4·HF):[14]