Properties of coal-tar pitches modified by sulfur addition, air blowing, and nitrogen blowing were compared to find an appropriate method of preparing a matrix precursor for carbon/carbon (C/C) composites. Raw and modified pitches were characterized by softening point, thermal analysis (TGA), elemental analysis, solubility in toluene and quinoline, and gel permeation chromatography. Both sulfur addition and air blowing very effectively increased softening point and coke yield by dehydrogenative polymerization of pitch molecules. Air-blown pitch, however, had less thermal stability than the pitch with added sulfur and showed more weight loss at high temperatures. Property changes in nitrogen-blown pitch were mainly induced by eliminating volatile matter of low molecular weight. Sulfur addition is suggested to be the most promising method for preparing matrix precursor because it had the highest yield among those with similar softening points.