The structures and dynamic formation processes of adlayers of 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine (TMPyP) on both bare Au(111) and iodine-modified Au(111) in perchloric acid have been investigated in detail by using in situ scanning tunneling microscopy (STM). Highly-ordered TMPyP arrays formed on iodine-modified Au(111), whereas disordered adlayers were consistently found on bare Au(111) surface. High-resolution STM images revealed the characteristic internal shape and orientation of each TMPyP molecule in ordered adlayers. Time-dependent in situ STM allowed direct observation of the dynamics of the self-ordering processes. Before the most stable adlayer was established in a relatively small domain, several structural changes were found to occur, including the formation of a one-dimensional ordered chain at an early stage and several phase transitions in the ordered adlayers. Once the most stable adlayer was formed as a nucleus in a domain, two-dimensional growth of the domain extended over the entire area of the terraces with the final packing arrangement.