A novel method was developed to prepare iron nanocrystallite by using coimplantation of Fe and C in copper and subsequent heat treatment. The formation process of iron carbide and iron granules was monitored by means of conversion-electron Mössbauer spectroscopy, and the particle size was determined by transmission electron microscopy. Cementite, , was formed after annealing at , then transformed to particles with a size of about 25 nm. Magnetic coercivities of 1.15 kOe and 0.37 kOe for the Fe granules have been observed at room temperature (RT) and 80 K, respectively. A retained carbon-enhanced effect was proposed to explain the strong coercivity at RT.