Phenolic fibers (PFs) were prepared by the crosslinking of heat-meltable spun filaments derived from melt-spinning of a novolac resin with well-controlled molecular weight of 2000 g mol(-1), in a combined solution of formaldehyde and hydrochloric acid. The reaction of the heat-meltable spun filaments with the solution of formaldehyde and hydrochloric acid was investigated. IR spectrometer, scanning electron microscopy (SEM), and electrical tensile strength apparatus were employed to characterize the change of functional groups, the distribution of crosslinkage in the interior and surface, and the tensile strength of PFs, respectively. The influence of different parameters during the curing reaction, such as formaldehyde and hydrochloric acid concentration, the effect of heating rate on the properties and structure of the cured fibers were examined. It was found that with a formaldehyde concentration of 18.5%, a hydrochloric acid concentration of 12% and a heating rate of 15.4 degreesC h(-1) homogeneous highly crosslinked phenolic fibers with the maximum tensile strength of 260 MPa were obtained. (C) 2004 Elsevier B.V. All rights reserved.