The morphologies of deposits on 15-mum diameter silicon carbide (SiC) fibers have been investigated with a scanning electron microscope (SEM) in co-flowing, propane/air laminar diffusion flames. The average size of the soot particles deposited in the luminous flame edge is strongly dependent on their position in a typical unconfined heavily sooting flame, but this position dependence is not discernible in a confined flame under a reduced oxidizer condition. The transition to soot from the condensed-phase deposits could be observed in the radial deposition of sooting flames. Two kinds of processes that mature soot particles are produced exist in a heavily sooting flame: one is the transition from the condensed-phase deposits; the other is the aggregation of the smaller soot particles (or chains of them) carried along the particle path line. The fiber-like structures, which are about 10-nm thick, were found outside the luminous flame surface, and are thought to be made under high temperature oxidation environment. (C) 2002 by The Combustion Institute.