Rheological properties of petroleum pitches are of major importance not only in the processing and final properties of carbon fibers, but they also helps in the selection of the raw material. In this work, a series of petroleum pitches with increasing contents of anisotropy was produced from decanted oil obtained from catalytic cracking process of petroleum, with the objective of investigate the rheological properties of these materials and its application on carbon fibers production. One of the produced pitches was centrifuged at high temperature with the objective of study the rheological properties of isotropic and anisotropic phases. The contents and textures of the obtained anisotropy were respectively analyzed by centrifugation at high temperature and by optical microscopy with polarized light. The molecular sizes of petroleum pitches were measured using the technique MALDI-TOF-MS (Matrix Assisted Laser Desorption Ionization Timeof- Flight Mass Spectrometry). The analyzed petroleum pitches exhibited an oligomeric nature and molecular masses up to 1500 Da were detected. Rheological characterization showed viscoplastic behavior of pitches and the measured flow curves were fitted using the Herschel-Bulkley viscosity function. Rheological analysis also showed the increasing of pitches elasticity with the progress of the heat treatment and the appearance of thixotropic behavior. The analytical techniques used in this work proved its efficiency on the study and characterization of petroleum pitches as carbon fibers precursors.