The series of ionic liquids based on triethanolammonium salts of dicarboxylic acids (oxalic, malonic and succinic) was synthesized, characterized by IR and H¹, C¹³ NMR spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Their structure was determined by single-crystal X-ray diffraction. It was found that triethanolammonium [(HOCH₂CH₂)₃NH]⁺ cations in salts of oxalic (1), malonic (2) and succinic acids (3) containing monoanions [OOC(CH₂)_nCOOH]⁻ (n = 0–2) have the endo conformation and the ammonium proton (H_am) resides inside the “lampshade” formed by three CH₂CH₂OH branches connected with nitrogen atom. The asymmetric cell of the second modification of the succinic acid salt (4) includes two triethanolammonium cations and a succinate dianion [(HOCH₂CH₂)₃NH]₂⁺[OOC(CH₂)₂COO]^{2 −}. In this salt (4) one CH₂CH₂OH branch of the triethanolammonium cation is rotated around the N[sbnd]C bond (endo-exo conformation) and forms infinite TEA chains. This pattern was firstly found in organic salts of TEA. The obtained results show that different structures of triethanolammonium cations in the salts of dicarboxylic acids have significant influence on the cation-anion interaction.