In the present study,19 soybean (Glycine max L.) cultivars were analyzed and found to differ considerably in aluminum (Al) resistance.The cultivars Zhechun No.2 (Al-resistant) and Zhechun No.3 (Al-sensitive) were selected for further analysis.Experiments were performed with plants grown in full nutrient solution for 30 days.Fourier transform infrared spectrometry (FTIR) with OMNI-sampler was applied to the direct determination of different varieties of soybean root tissues,treated with aluminum in a dose-and time-dependent manner plus exogenous citric acid.Then the characteristic absorption peaks of spectra were analyzed and some differences in the FTIR spectra among samples were found from the comparison of the spectra.Results showed that the intensity and the shape of absorption peaks of their FTIR spectra exhibited some differences between different kinds of soybean and different treatment,especially around 1 057,1 602,2 927 and 3 292 cm^-1,which mainly reflected the content variety of protein,glucide,nucleic acid and so on.Thus it could be concluded that the effect of aluminum stress and existence of exogenous citric acid did not change the component of chemical substance in soybean roots,although the content of certain substance varied.The two dimensional discriminates analysis chart was drawn by the ratio of area at 2 927 cm^-1 to that at 3 297 cm^-1 as the abscissa vs the ratio of area at 1 057 cm^-1 to that at 1 602 cm^-1 as the vertical,to discover the difference between the treatment of aluminum plus exogenous citric acid and that of single aluminum.Result indicates that the difference in the shape of absorption peaks of FTIR spectra became smaller and that presumed the content variety with different treatment was not remarkable under the condition of exogenous citric acid,especially in Zhechun No 3.From all mentioned above it is made clear that exogenous citric acid could really ameliorate distinctly the effect of aluminum on soybean roots which was detected by direct determination of FTIR spectrum,giving the fact that FTIR could reflect the ameliorating effect of exogenous organic acid on plant tissue under aluminum stress.