Dielectric constant, ε', dielectric loss factor, ε", electric modulus, M, and ac conductivity, σ_ac, of pure CPVC and that stabilized with 10 wt% of phenyl maleimide, PM, have been carried out. The dielectric properties have been studied in the temperature and frequency ranges; 310 K - 450 K and 1 kHz- 4 MHz, respectively. The incorporation of 10 wt% of PM as stabilizer for CPVC leads to reduce its Tg from 405K to 378K at 10 kHz. PM molecules within CPVC structure reduce the double bond, stabilizer effect, and cause the widely spacing between CPVC main chains, plasticizer effect.  Three dielectric relaxation processes namely ρ, α', and α were observed for pure CPVC. The first process was explained based on space charge formation or Maxwell-Wagner-Sillers, MWS, polarization. The second one is due to the segmental motion of the branching of CPVC. The third process occurs around the glass-rubber temperature, Tg, and is related to the micro-Brownian motion of the main polymer chain. Electric modulus and ac conductivity reveal that the conduction mechanism of CPVC is follow the correlated barrier hopping, CBH, while stabilized sample exhibits a quantum mechanical tunneling, QMT, type conduction.