The present work deals with the preparation of carbon fibers from polyacrylonitrile (PAN) fibers. The chemical composition and physical properties of the starting fibers were determined. The PAN fibers were stabilized in air at the temperatures (230, 270, and 300 degrees C) with the heating time from 40 to 420 min. The effects of both final stabilization temperature and heating rate on the chemical and physical properties of the prepared stabilized fibers were studied. The chosen stabilized fibers samples were carbonized in argon atmosphere at the temperatures (1000, 1200, and 1400 degrees C) with different heating rates 5, 10, 15, and 20 degrees C min(-1). The effects of both carbonizing temperature and heating rate on the weight loss, density, elemental composition, and IR absorption spectra of carbonized fibers were also studied. The fiber sample, which was carbonized at 1400 degrees C, contains 97.55% carbon, 1.75% nitrogen, and 1.4% hydrogen. This means that carbonizing the stabilized fibers at 1400 degrees C in argon atmosphere is suitable to get oxygen-free carbon fibers. Therefore, the used carbonizing temperature in the present work (1400 degrees C) is suitable to produce moderate heat-treated carbon fibers with the heating rate of 15 degrees C min(-1). The modulus of the prepared carbon fibers was compared to that of industrially produced fibers using the results of X-ray analysis. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2074-2083, 2012