PURPOSE: To prepare pitch which produces carbon fiber with a high elastic modulus, by heat treating petroleum heavy oil, removing insoluble matters and then distilling out low-boiling fractions.

CONSTITUTION: A petroleum-based heavy residual oil having a boiling point of 400°C or higher (as under normal pressure) and sulfur content of 1.5wt% or lower, is heat treated. After removal of insoluble matters by heating at a temp. below 380°C, fractions having a boiling point below 400°C (as under normal pressure) are removed by vacuum distillation to produce pitch with a quinoline- insoluble content of 7W18wt% and a toluene-insoluble content of 70W85wt%. The resultant pitch which has so far been considered to be unsuitable as raw material for conventional processes, is spun quite readily and produces carbon fiber with a high elastic modulus.