Cellulose acetate (CA) membranes were modified by nano-silicon dioxide (n-SiO2), and they were exposed to ultrasonic waves at a frequency of 35 kHz. The effect of sonication on their water sorption tendency and permeation capability was investigated. The characterization of the membranes was done by FTIR and SEM analysis, and the hydrophilic character of the membranes was deduced by swelling studies and contact angle (CAn) measurements. Permeation studies of the membranes were performed by using the diffusion method and theophylline was used as a model chemical in the permeation studies. The results indicated that beside the high hygroscopic property of n-SiO2 the presence of n-SiO2 in CA membranes did not significantly improve their hydrophilicity; however, when they were exposed to sonic waves, it was determined that the sonication effectively enhanced their water sorption capacity and permeability.