The stabilization behavior of poly(acrylonitrile)(PAN) fibers was monitored by measuring the changes in density, structural aspects and mechanical properties during continuous stabilization processing. The effects of the processing conditions, such as the speed of precursor supply, yam tension, oxidation temperature, and treatment time, on the mechanical properties of the final carbon fibers were also examined. The oxidized PAN fibers were analyzed by measuring the density and aromatization index. The change in yam tension had critical effects on the final mechanical properties of the carbon fibers. The maximum mechanical properties of carbon fibers were obtained by properly controlling the stabilization conditions.