Compatibility of poly( vinyl chloride) (PVC) with liquid natural rubber (LNR) and epoxidized liquid natural rubber (ELNR) has been studied by solution viscometric methods. The relative viscosity versus composition plots for PVC/LNR and PVC/ELNR-20 blends are found to be nonlinear. The corresponding intrinsic viscosity values show negative deviation from ideal behavior when plotted against composition. The modified Krigbaum and Wall parameter, Delta b, also shows negative values for all compositions of these blends studied. The results indicate that PVC/LNR and PVC/ELNR-20 blends are incompatible systems. On the other hand, PVC/ELNR-50 blends yielded Linear plots when relative viscosity was plotted against composition. The intrinsic viscosity composition plots for this system showed positive deviation from ideal behavior. The Delta b values are positive for all compositions of these blends studied. These results are characteristic of a compatible blend system. Hence it is concluded that liquid natural rubber can be made compatible with PVC when the former is epoxidized to a sufficient level.