This paper investigates the effect of polyhedral oligomeric silsesquioxane (POSS) nanoparticle inclusion in cellulose acetate (CA) membranes. The synthesis of a novel CA-anchored nanoparticle additive (CAPOSS) is described. Membranes were fabricated with no additive, or either the POSS or CAPOSS as an additive at different weight percent loadings. Nanoparticle dispersion was investigated using scanning electron microscopy. Dynamic mechanical analysis was used to investigate the mechanical strength of the nanocomposite membranes. The effect of nanoparticle inclusion on the filtration properties and compaction behavior of the membranes was also investigated. Compared to the CA control, nanocomposite membranes exhibited superior flux and compaction resistance, and decreased salt rejection and mechanical strength.