Abstract: The toluene soluble part of coal tar pitch (TS) was co-carbonized with waste polystyrene (WPS) to produce mesophase pitch. Results showed that the properties of the mesophase were improved greatly due to the eutectic effect. The solubilities of the TS mesophase pitch and TS-WPS mesophase pitch were 10 and 52 wt. % respectively. The anisotropic volume fractions of the TS mesophase pitch and TS-WPS mesophase pitch were 65% (coarse mosaic texture) and 100% (flow domain texture) respectively. Apparent viscosities showed that the mesophase pitch was changed from thixotropic to unthixotropic by adding WPS to TS. FT-IR and ¹H-NMR spectroscopy showed that an alkylation reaction took place accompanied by an increase of methylene groups when WPS was added to TS. The increase of alkyl groups led to an assembly of mesogen molecules, resulting in a eutectic effect.