Herein we report the atomic model of pseudomorphic Fe monolayer on Ru(0001) surface analyzed by low energy electron diffraction (LEED) followed by the formation of c(4×2) structure upon exposure to oxygen. After deposition of the Fe overlayer on Ru(0001) surface at room temperature, the prepared surface was exposed to molecular oxygen (O2). When 2 Langmuir of O2 is introduced at room temperature on the prepared Fe(111)/Ru(0001) surface, the pseudomorphic p(1×1) structure of the Fe monolayer on the Ru(0001) surface changes to c(4×2) structure.