Mesophase pitch (MPP) has a high carbon yield and excellent graphitizability, compared with commercial coal tar pitch (CTP), which make it suitable for the preparation of C/C composites. In this paper, two MPP were prepared by heat-treatment of two coal tar pitches (CTP and modified coal tar pitch (MCTP)) in the presence of nitrogen. Elemental analysis and FTIR were used to monitor the change of chemical structures of MPP transition from CTP and MCTP. The pyrolysis behaviors of CTP and MCTP were studied by means of thermal analysis (TG and DSC). The morphologies of MPP were inspected by optical microscope. The structures of the MPP were characterized by XRD. The results show that there are more alkyl functional groups existing in CTP and MCTP than in MPP, and MPP has a higher C/H ratio than CTP and MCTP, which indicate MPP formation predominantly polycondense aromatic and release the alkyl functional groups. An endothermic band due to volatilize light compounds around 290 °C, two exothermic peaks at 430°C and 490 °C were characteristic of polymerization reactions, exothermic peaks of MCTP are higher than that of CTP because the former has a higher reaction active for its more alkyl side chain. The optical texture of MPP from CTP is mosaics texture, while from the MCTP is flow domains texture. (002), (101) peaks of graphite occur on XRD patterns, the peaks of MPP from MCTP are higher and narrower than MPP from CTP, which indicates the former is more graphitizability than the latter.