Quantitative and qualitative analyses of chlorine-containing elastomer blends, like neoprene rubber/chlorosulfonated polyethylene and neoprene rubber/nitrile-polyvinyl chloride, with carbon black and other fillers, are complex and confusing because the blends contain the same carbon-chlorine moiety. Various interfering phenomena by fillers, co-curing by the common ingredients, and uncertainty in functional group analysis make the determination of the ratio of component elastomers in chlorine-containing elastomer blends very difficult or sometimes almost impossible by Fourier transform infrared and thermogravimetric analysis techniques. However, differential scanning calorimetry (DSC) and supportive differential thermogravimetry (DTG) are very useful techniques to assess such complex materials. Enough flexibility associated with specific heat (from DSC) and response zone (from DTG) can avoid the interfering effects. The DSC-DTG technique thus can be an effective tool to determine the ratio of component polymers in chlorine-containing elastomer blends.