Mass and heat transfer in square ducts with one side containing a porous wall were simulated using large eddy simulation (LES). Increased wall normal turbulent intensity was observed along the porous wall compared to the smooth wall. Depending on the wall permeability the fluid elements penetrated to different depth resulting in enhanced mass and heat transfer rates. The larges effect was obtained for mass transfer in liquids with up to 20 times larger mass transfer rate, compared to smooth surfaces. An increased penetration into the porous wall was obtained with more open porous structure and with fluids having high density and low viscosity. Most benefit of the porous walls is obtained for fluids with high rho/mu ratio and high Pr or Sc numbers i.e. for mass transfer in liquids. (C) 2013 Published by Elsevier B.V.