Single crystals of dilithium‐acetylenedicarboxylate‐dihydrate, Li2ADC·2H2O (1), were isolated from a solid product formed by isothermal evaporation of an aqueous solution of LiOH und acetylenedicarboxylic acid (H2ADC). 1 crystallizes in the triclinic space group P1 with Z = 2. LiO4 tetrahedra are interconnected by ADC2– anions and water molecules to form a 3D polymeric structure. Coupled TGA and DTA measurements show that 1 loses its two water molecules above 100 °C. Heating a polycrystalline sample of 1 at 140 °C for 2 h in an argon atmosphere leads to a significant change of the powder diffraction pattern indicating the formation of the new anhydrous coordination polymer dilithium‐acetylenedicarboxylate, Li2ADC (2). Its crystal structure was solved and refined from X‐ray powder diffraction data. 2 crystallizes in the orthorhombic space group Fddd (Z = 8). LiO4 tetrahedra are interconnected by ADC2– anions to form a 3D polymeric structure.