The aggregative behaviors of hydroxypropylcellulose (HPC) molecules in aqueous solution and on substrates have been observed by employing laser light scattering (LLS) and, after deposition on a mica surface, atomic force microscopy (AFM). LLS studies showed that the HPC molecules formed large aggregates through self-association when the concentration of the solution was above the critical concentration c(t). AFM measurements revealed that when a dilute aqueous solution of HPC molecules was deposited onto a mica substrate at a temperature below its lower critical solution temperature (LCST) thin nanofibers were formed with a height of 0.9 nm, whereas thick nanofibers were formed when an aqueous solution of HPC molecules was deposited onto a substrate above its LCST. Furthermore, the growth of nanofibers led to the formation of fan structures.