Mountain top removal/valley fill (MTRVF) interrupts stream structure and function by burying headwaters while leaving lower portions of the stream channel intact.  We measured leaf breakdown to explore whether organic matter processing is altered by the conditions MTRVF imposes on streams.  We placed red maple and white oak leaf packs in five streams draining MTRVF fills and five reference streams in central West Virginia in December 2007.  Sample packs were retrieved approximately monthly until June 2008, dried, weighed, and AFDM determined. Leaf shredding macroinvertebrates were removed from the leaf packs, identified, and counted. Ergosterol, as a measure of fungal biomass, was determined.   We also measured fine and coarse sediments accumulating on the leaf packs once during the study. We found significant differences in leaf mass lost between mined and reference streams, for both leaf species.  Our results suggest that most factors influencing organic matter processing in steams, from hydrology to macroinvertebrate feeding, are affected by MTRVF, such that breakdown rates are slowed and expected differences in breakdown rates between leaf species were reduced.