A thermotropic acetylene-terminated liquid-crystal monomer, 2-methyl-1,4-phenylene bis(4-ethynylbenzoate) (MPBE), was prepared and used as a modification composition to react and cocure with a silicon-containing arylacetylene (PSA) oligomer for improving PSA resin. The curing behavior of the PSA-MPBE resins were characterized by differential scanning calorimetry and Fourier transform infrared spectroscopy. The microstructure and morphology of the PSA-MPBE resins were investigated by scanning electron microscopy (SEM) and transmission electron microscopy. Their dynamic mechanical properties and thermostability were measured by dynamic mechanical analysis (DMA) and thermogravimetric analysis. The results indicate that the thermotropic acetylene-terminated liquid-crystal monomer melted into a schlieren texture. MPBE and PSA could copolymerize to fix the mesogenic domain in the crosslinked network and form a homogeneous-phase sea-island structure, which improved the rigidity and toughness of the materials. DMA showed that the storage modulus of the PSA-MPBE resins increased by about 400 MPa compared to the those of the pure components. The SEM experiments showed a noticeable change in the morphology, from a typical brittle fracture for the pure PSA to microplastic deformation behavior for the PSA-MPBE resins.