For the purpose of characterizing the evolution of water-extractable organic matter (WEOM) during the biostabilization of municipal solid waste (MSW) and investigating the correlation between biostability and WEOM characteristics, this study conducted 100-day investigation on biostabilization of MSW and applied various analytical approaches to characterize WEOM. The results showed that the respirometric activity of MSW was reduced by 93% to 10.7 mg kg(-1), and the dissolved organic carbon concentration of WEOM kept steady at around 4.0 g kg(-1) after day 44, when the MSW was considered to be stabilized. Moreover, the aromaticity of WEOM significantly increased and the high-molecular weight fraction became the main part of WEOM. Being highly related to the biostability of MSW, the excitation-emission matrix spectra indicated the stability by the fluorescence regional integration technique either by the presence of specific Ex/Em maxima (with wavelength pair of similar to 288/455) or by the rapid increase of normalized excitation-emission area volumes with respect to the humic substances. (C) 2008 Elsevier B.V. All rights reserved.