Polymer blends and composites are widely used in automobile parts. In these compounds, the most important factor is the blend ratio. So, we have carried out the quantitative analysis for the PC/PBT blend using TGA and new analysis method of NMR spectroscopy. A further study, we also studied prediction model equations of mechanical properties of tensile, bending and impact strength from the compositional results. In conclusion, this advanced analytical technique will help us to develop new products and deal with field claims in automobile industry.