The effect of heating temperature on the magnetic property of alpha-Fe nanoparticle produced by thermal decomposition method has been investigated. The Fe (2+)- oleate(2) ligand complex was annealed at 400 degrees C in pyrex tube under 10(-2) torr for 2 hrs, and then reduced at a different temperatures under Ar+ 4% H-2 mixture gas atmosphere. The magnetic property of alpha-Fe nanocrystallite was affected with the different heating temperatures. The structure and properties of prepared alpha-Fe nanoparticle was characterized by TGA, XRD, TEM, and VSM.