Understanding the distribution and activity of sulfate reduction at hydrothermal vents requires a more thorough interrogation of the community ecology and metabolic activity of vent hosted microorganisms in the context of the extreme physico-chemical environment. To date, many studies have quantified rates of sulfate reduction in hydrothermal-influenced sediments and vent isolated microorganisms, but only one study of sulfate reduction exists for hydrothermal deposits. Here we present rates of microbially-mediated sulfate reduction –as determined via 35S tracer studies- from three distinct hydrothermal deposits recovered from the Middle Valley vent field on the Juan de Fuca Ridge. We further evaluate these rates in the context of the in situ geochemistry and microbial community structure of each chimney to better constrain linkages between phylogeny and function. <p> Middle Valley hydrothermal deposits Chowder Hill, Dead Dog, and Needles collected July 2010 AT15-67 on Alvin Dive 4625.