Miscibility studies of poly(vinyl pyrrolidone)-polystyrene and poly(vinyl pyrrolidone)-poly(methyl methacrylate) in mixed common solvent (dimethyl formamide + cyclohexanone) have been carried out in different percentages of the blend components. The ultrasonic velocity, viscosity, density, and refractive index have been measured at 30 degrees C. The interaction parameters have been obtained using the viscosity data to probe the miscibility. The obtained results have been confirmed by the ultrasonic velocity, density, and refractive index.