Abstract The effect of strain on N 2 dissociation on Fe surfaces has been investigated by the use of density functional calculations (DFT). To study the strain effect we did calculations on fcc-Fe(1 1 1) surfaces with different lattice constants. These calculations show that by expanding the surface lattice constant, the barrier for the N 2 dissociation is lowered. The same effect can be achieved by having a pseudomorphic Fe layer on a Ru(0 0 0 1) surface. The dissociation barrier on the strained Fe overlayer is lower than on the unperturbed bcc-Fe(1 1 0) surface by an amount given primarily by the strain in the overlayer. Calculations on another closed packed Fe surface, bcc-Fe(1 1 0) are also reported.