The theological behavior of mesophase pitches containing multi-walled carbon nanotubes has been investigated using a cone-plate-type rheometer at various temperatures. In the case of the pure mesophase pitch, for low shear rates, the shear viscosity decreased with increasing rate of shear (a shear thinning behavior). However, for higher rates of shear (1-10 s^-1), the steady shear flow curves exhibit a plateau region in which the viscosity is independent of shear rate. Also, in the shear thinning region, the shear viscosity decreases at almost the same rate for pitches within these temperature ranges. If MWNTs do not interfere with the structure and molecules of the mesophase pitch, the shear flow curves of a MWNT-dispersed pitch should be similar to that of the pure pitch. The viscosity of MWNT-dispersed pitch over the whole range was much higher than that of pure (unmixed) mesophase pitch. The viscosity of 5 wt% MWNT mixed pitch decreased sharply as the shear rate increased when compared to 1 and 2 wt% MWNT mixed pitch. The shear viscosity decreased at a faster rate in the shear thinning region (e.g., at low shear rate). The value of the viscosity shear activation energy of each pitch decreased as the WMNT content increased, because the MWNTs act as impurities during shearing.