Poly(acrylonitrile) (PAN) was solution blended with poly( n-butyl methacrylate) (PnBMA) in various proportions. Compatibility in these blend systems was analyzed using ultrasound. The ultrasound velocity and attenuation results show that the two polymers formed a compatible blend. Viscosity and other derived parameters like free volume and internal pressure of the blends show that PAN form into an ideal blend with PnBMA in the compositions of 60:40 and 40:60.