The rheological behavior of mesophase and isotropic pitch blends were examined using capillary and coneplate viscometers to determine the spinnability. The mesophase synthesized from naphthalene and coal tar pitch modified with benzoquinone were used. The individual component of the mesophase pitch or the isotropic phase pitch showed excellent spinnability but the spinnability of the blends decreased as the composition approached 50 wt.%. The variations of the spinnability were explained based on the mechanisms of capillary break-up and cohesive brittle fracture. The fracture of the spin line was caused mainly by capillary break-up originating from the high interfacial tension between the two separated phases; the behavior was more severe in the lower shear rate region, i.e. the elasticity dominant area. The spinnability of the two phase blends could be improved by maintaining the melts under the viscosity dominant condition by adjusting the shear rate and temperature.