Poly(ethylene terephthalate) fiber was pretreated with biphenyl/methylene chloride and other solutions. Other solutions used in this experiment were methylene chloride, perchloroethylene/methylene chloride, biphenyl/water and hiphenyl/perchloroethylene. The dyeing behaviors of the pretreated fibers with C.I. Disperse Red 4 in water were studied with reference to changes in the matter properties of fiber. Also density and X-ray diffraction of the fibers were investigated as measure of crystalline region. The results obtained are briefly discussed in terms of the plasticization of the fiber structure and penetraing biphenyl volume formed during the pretreatment and pretreated time and temperature. The results are as follows; 1) The crystalline growth of PET fiber treated with 5% biphenyl/methylene chloride was also greater than that treated with other solutions, and this tendency was increase with volume of added biphenyl. 2) Equilibrium dye absorption and initial rate of dyeing of PET fiber treated with 5% biphenyl/methylene chloride were greater than those of sample with other solution. 3) The diffusion and dye affinity of PET fiber treated with 5% biphenyl/methylene chloride were greater than those of sample with other solution. I think that dyeing method of energy conservation of pretreated PET fiber is dyeing PET fiber pretreated with 5% hiphenyl/methylene chloride.