The initial stages of the nitridation processes on Si(lll) have been investigated by scanning tunneling microscopy. Two nitridation processes are tried : one is an exposure to a clean Si(111)7x7 surface at room temperature followed by annealing, and another is an exposure on the hot substrate, In either case, the initial reaction occurs at the center adatom sites and they tend to pair with each other across the adjacent dimer row, At high coverage, very flat monolayer Rims with an 8x8 superstructure are clearly observed, the surface of which seems to contain misfit dislocation presumably due to relaxation of the surface stress.