An experimental study for isotropic pitch materials prepared from cracking oil residues has been carried out to clarify the Theological properties in the molten state. The softening point, thermal expansion coefficient, viscosity and the viscoelastic moduli were measured. The aromatization index of the isotropic pitches was estimated from the element analysis (C and H), density, and the NMR measurements. The activation energy for shear flow which was estimated from the temperature dependence (100°C to 150°C) of the steady shear viscosity was 40 kcal/mol. The softening points, thermal expansion coefficient and the activation energy were correlated to the aromatization index. The steady state shear viscosity was described to be proportional to the molecular weight with the 40th power. The frequency dependences of the dynamic moduli were similar to those of monodisperse linear polymers.