Abstract: In a method of manufacturing carbon fiber with less uniformity of physical strength in the longitudinal direction, an oil additive in a volatile medium is applied to an organic fiber after it is removed from a container and while the volatile medium has not completely evaporated from the fiber, and before the fiber is fed to a flameproofing furnace.

Abstract: A carbon fiber of high strength is disclosed, each filament of which is substantially circular in its cross-section but which has circumferential ruggedness which extends in parallel to an axis of the filament to form pleats. The ruggedness has a depth of more than 0.1 .mu.m.The carbon fiber is prepared by extruding a spinning solution of an aqueous polyacrylonitrile/pure zinc chloride solution of a specified polymer content into a coagulating bath at a specified draft ratio, followed by washing, drying and stretching at a total stretching ratio of 10-20 folds to form a precursor which is then subjected to conventional stabilizing and carbonizing steps.