Samples with 5.1%, 9.8% and 15.3% HbA1c were extracted from normal subjects and patients with slight and serious diabetes respectively. Extended x-ray absorption fine structure spectra of Fe K absorption were collected at the EXAFS experimental station of the Beijing Synchrotron Radiation Facility. The step-by-step fluorescent mode was employed with a count time of 10 s per point. Several independent scans were averaged to eliminate the statistical noise. Reference backscattering amplitudes and phaseshifts were calculated using the curve wave theory (FEFF code) of EXAFS. Apart from the nitrogen neighbours around the central iron atom, oxygen neighbours are also found. The Fe-N bond length increases by about 0.02 Å for the sample with 15.3% HbA1c compared with the others, but the Fe-O bond length is almost unchanged. With increasing of HbA1c concentration, the content of Hb increases and the content of HbO2 decreases. This demonstrates that the glycosylation of haemoglobin will decrease its ability to carry oxygen.