PS/PPSQ blends with different compositions were prepared by two methods : (1) casting film of PS/PPSQ from the solution of two polymers, and (2) PS/PPSQ blends by in situ polymerization. After studying by solid-state NMR, PS and PPSQ in the casting films are miscible on the scale of several thousand nanometers. Miscibility of PS/PPSQ blends obtained by the second approach was investigated by DMA, SEM, x-ray energy spectrometer, x-ray diffraction, and fluorescence techniques. Only one glass transition temperature could be observed in their DMA curves. There are two phases observable in their SEM micrographs. X-ray diffraction patterns and fluorescence excited spectra of this blend indicate that there is some interaction between molecules of PS and PPSQ in both the continuous phase and dispersed phase. PS and PPSQ in the in situ blends are partially miscible when the percentage of PPSQ is not more than 10%.