Due to a consideration of Al detoxicification by simple carboxylic acid, the interaction between aluminium ion (Al³⁺) and three dicarboxylic acids (oxalic acid (OX), malonic acid (MA) and succinic acid (SU)) under an acidic condition was investigated using ¹³C and ²⁷Al NMR techniques. Based on deconvolution of the ²⁷Al NMR spectra and quantitative ¹³C NMR spectra, the structure of each complex was elucidated. Especially, we focused on the peak assignments of ²⁷Al NMR spectra by combining of the results of quantitative ¹³C NMR spectra. In the OX system, the peak at 16 ppm in the ²⁷Al NMR spectrum originates from Al(OX)₃³⁻ and Al(OX)₂⁻, and the ratio of each complex depends on the OX/Al molar ratio. In the MA system, the three complexes (Al(MA)₂⁻, Al(MA)₃³⁻ and Al(MA)⁺) are represented in the peak at 2 ppm in the ²⁷Al NMR spectrum. The assignment of peaks in the ²⁷Al NMR spectra in this study differs from those described in previous papers.