Microwave measurements have been carried out on the industrially important rubber and polymer materials to study their dielectric behavior in X and K bands using microwave test benches equipped with Klystron and Gunn oscillators respectively and guided with rectangular wave guides. A decrease in dielectric constant with increase in microwave frequency has been observed for all samples. Some rubber materials were reinforced with carbon black as the reinforcing filler and vulcanized with sulphur as the principle vulcanizing agent in the industrial lab and their change in dielectric behavior was studied at microwave frequencies. The rubber materials after being reinforced and vulcanized have a high dielectric constant, low dielectric strength and hence have better electrical conductivity. One of the polymers Nylon 66 also showed an increase in dielectric constant after being reinforced with 30% glass fibre. To improve the applications of rubber derivatives, a blend is made between any two already available rubber materials which are thermodynamically compatible to one another. The dielectric behavior of two such polymer blends viz, NR+BIIR and NR+Reclaim was studied in the microwave frequency region. From the results obtained, it is observed that the electrical conductivity of the rubber derivatives increase after blending. Hence blending is a very important technique to improve the electrical properties of rubber materials.