Neptunium (IV) oxalate[1] is an inorganic compound, a salt of neptunium and oxalic acid with the chemical formula Np(C2O4)2.

[2] The compound is slightly soluble in water, forms crystalline hydrates—green crystals.

[3][4] Neptunium(IV) oxalate is formed by the oxalic acid precipitation of neptunium (IV) solutions:[5] Neptunium(IV) oxalate forms a crystalline hydrate of the composition Np(C2O4)2 • 6H2O with green crystals.

It is insoluble in acetone, and slightly soluble in water.

[6] Neptunium(IV) oxalate decomposes on heating:[7] Neptunium(IV) oxalate is used as an intermediate product in the purification of neptunium.