For a long time, understanding the mechanisms of impurity-promoted embrittlement in iron and the consequent cohesion(decohesion) effects has been a challenge for materials scientists. The role alloying elements play in impurity-promoted embrittlement is important due to either their direct intergranular cohesion(decohesion) effects or effects upon embrittling potency of other impurities. Some alloying elements like Pd and Mo are known to be helpful for intergranular cohesion in iron and some other alloying elements like Mn are known to segregate to and weaken iron grain boundaries dramatically. There have been intensive investigations on these mechanisms for a long time and especially, with the progress in computing techniques in recent years, calculations on more realistic models have become possible[2–4]. In this paper we briefly present our studies on some selected alloying-element/iron grain boundaries(GB) and free surface(FS) systems. The effects of Pd, Mo, Mn and Cr on the Fe Σ5 (031) grain boundary and its corresponding (031) free surface are examined, using a combination of molecular dynamics(MD) and first-principles electronic structure calculations. Section 2 gives a brief introduction to the methods used and Section 3 gives the main results.