The extent of compatibility of the blend solutions poly(vinyl chloride)liquid natural blends (PVC-LNR), PVC-expedited LNR-20 (PVC-ELNR-20), and PVC-ELNR-50 has been studied using an ultrasonic technique. The variation of ultrasonic velocity with composition is nonlinear in the case of blends of PVC-LNR and PVC-ELNR-20, showing incompatibility. The ultrasonic velocity versus composition plot for PVC-ELNR-50 showed linear behavior showing compatibility. The above behavior was confirmed by heat of mixing calculations as well as ultrasonic attenuation measurements.