Cellulose acetate (CA) and CA blended with molybdenum trioxide MoO3 nanoparticle at concentration of (0.0, 0.25, 0.5& 1.0 wt. %) prepared by casting method. Ac conductivity and dielectric properties were studied. Our results indicated that the conduction mechanism of CA and CA blended with different concentration of MoO3 nanoparticle is controlled by the correlation barrier hopping (CBH) model. The ac conductivity was observed to increase by adding MoO3 nanoparticle which explained by the network formed as the nanoparticle gets closer to each other as the concentration increase. The maximum barrier height was calculated and found to decrease by increasing MoO3 nanoparticle from 0.15 t0 0.12 eV. The analysis of the dielectric constant and dielectric loss suggested that their behavior can be explained by Maxwell–Wagner–Sillar type polarization at high frequency. At low frequency the polarization is high as a result of interfacial polarization. Arrhenius equation was used to calculate the activation energy of relaxation which found to decrease by increasing MoO3 nanoparticle.