A low-cost grade natural rubber (STR20 NR) was used for partly substituting elastomeric chlorinated polyethylene (CPE) and then cured by sulfur. Rheological properties of blends with various blend composition ratios under oscillatory and steady shear flows were investigated. Cure behavior is found to be promoted with increasing NR content. The viscoelastic behavior of CPE/NR blends, as determined from the Rubber Process Analyzer (RPA2000), is controlled strongly by blend composition. Uncured blends show relatively poor storage modulus associated with high damping factor probably due to the thermal degradation of NR phase. By contrast, after curing the NR phase in blends, bulk rheological properties change remarkably. Blends with NR as a major component reveal frequency-independent behavior with a broad linear viscoelastic (LVE) region. Flow properties under capillary shear of uncured blends agree well with those under oscillatory shear, i.e., the greater the NR content, the lower the apparent shear viscosity. Surprisingly, even without the elimination of elastic effect by the Bagley correction, it is still possible to superimpose plots of complex viscosity against test frequency over those of apparent shear viscosity against wall shear rate, which are different from the rheological properties of CPE blended with premium grade of NR (STR5L).