An experiment was conducted to determine the fractions of molecular weights (MW) and the biodegradability of dissolved organic matter (DOM) in mature composts derived from dairy cattle manure (DCM), kitchen waste (KW), cabbage waste (CW), tomato stem waste (TSW), municipal solid waste (MSW), green waste (GW), chicken manure (CM), sludge (S), and mushroom culture waste (MCW). There were distinct differences in the concentration and MW fractions of DOM, and the two measures were correlated. Fraction MW > 5 kDa was the major component of DOM in all mature composts. Determined 5 day biochemical oxygen demand (BOD5) of DOM was correlated to the concentration of DOM and all MW fractions except MW > 5 kDa, indicating that the biodegradability of DOM was a function of the content and proportion of fraction MW < 5 kDa. This study suggests that the amount and distribution of low MW fractions affect DOM biodegradability. (C) 2014 Elsevier Ltd. All rights reserved.