Fourier transform infrared (FTIR) spectroscopy was used to study the HEp-2 cells irradiated by XRay with different dose. The results showed that there were significant discrepancies in the different dose groups′ cells. Compared with the control group, the contents of protein, nucleic acid and fat in the higher dose groups were decreased obviously. The wavenumbers of some peaks were shifted when irradiation dose was increased gradually. For example, there were redshift 3~16 cm-1 in the absorption peak around 3314 cm-1; the peak of 1454 cm-1 was blueshifted by 3cm-1; the peak of 1400 cm-1 was redshifted by 3cm-1; the peak of 2847 cm-1 was blueshifted by 4~8 cm-1. In addition, from the relative intensities ratios of I1654／I1542，I1454／I1400，I2958／I2847, the contents and frameworks of protein, nucleic acid and fat were changed most intensely in the 8Gy dose group, which was compared with the control group. It suggested that the cancerization of the 8Gy dose group′s cells was the lowest in these groups. All of the results may offer some experimental evidences in search of the optimum irradiational dose of X-ray.