The studies of solvent mass uptake and swelling dynamics of CdS-polyacrylamide nanocomposite ultrathin films in saturated solvent (H2O) vapor were carried out. The nanocomposite material was synthesized via a chemical route. The films were prepared by spin-coating on silicon substrates. The mass uptake behavior of solvent molecules into the films, studied using the gravimetric method, was found to be film thickness dependent and of non-Fickian in nature. The swelling dynamics was studied using X-ray reflectivity as a function of swelling time. As a result of the polymer nanoparticle interaction, the dynamical behaviors of mass uptake and swelling for the nanocomposite films were observed to be widely different from our earlier observation for the pure polymer films. A mathematical model was proposed to describe the swelling behavior of the nanocomposite films in terms of the combination of a fraction of polymer molecules with somewhat restricted freedom of movement and the ones that are free. About 5-9% chains were found to have restricted motion to describe the swelling of the nanocomposite films which was close to the volume fraction of the CdS particles in the composite. The dynamical constants for the swelling of the restricted chains were found to be orders of magnitude different than those of the free chains.