Reduction capacity ( RC ) is an important index to evaluate the redox ability of dissolved organic matter. In order to determine the RC, hydrophilic organic fractions ( HyI ) isolated from dissolved organic matter extracted from the uncomposted and composted samples were used as electron donators and mediators, and three kinds of irons were chosen as electron acceptors. The results showed that, the RC values from the composted sample were 15. 88, 13. 41 and 51. 45 mmol e -/mol C for the electron acceptors Fe2(SO4)3, Fe(NO3)3 and FeCit, respectively, which were higher than the corresponding values (13. 45, 11. 77 and 43. 16 mmol e-/mol C) from the uncomposted sample. The electron acceptor type shows a dramatic influence on the RC value of HyI. The RC value determined by FeCit was obviously higher than that measured using Fe2( SO4 ) 3 and Fe( NO3 ) 3 , and the microbial reducing capacity of the HyI was lower than the corresponding native reducing capacity. By analyzing the special absorbencies ( SUVA254 and SUVA280 ) , absorbance ratios ( A2/A3 and A4/A6 ) and integrated area from UV-vis spectra, it can be found that the RC was affected by aromatic degree, unsaturated conjugated structure, and molecular weight. Excitation-emission matrix spectra coupled with regional integration analysis showed that the relative content of humic-like substances ( humic-like acids and fulvic-like acids) was the main factor influencing the RC value of HyI. The results obtained can be used to characterize the redox properties of HyI, and reveal its role in the transformation and degradation of pollutants during composting.