An energy-efficient recycling technique was developed using various reactive gases and pyrolysis periods. An activation energy study of the polymer matrix decomposition was employed in order to obtain optimal pyrolysis conditions as a function of reactive gases. From the results, the total energy consumption for matrix pyrolysis at the low temperature region (under 400 degrees C) was the smallest with the carbon dioxide atmosphere. To remove all carbonaceous residue, a two-step pyrolysis technique was used, consisting of a low temperature decomposition (carbon dioxide at 400 degrees C) and high temperature decomposition (superheated steam method at 700 degrees C). Properly recycled carbon fibers were obtained after more than 40 min of superheated stream treatment. The mechanical strength of the recycled carbon fibers was measured using a single fiber tensile test, and it was found that all recycled fibers had over 80% of the strength of virgin carbon fibers.