Bioavailability of oral drugs can be limited by an intestinal excretion process mediated by P-glycoprotein (P-gp). Polyethylene glycol (PEG) is a known P-gp inhibitor. Dispersion of Famotidine (a P-gp substrate) within PEGylated nanoparticles (NPs) was used to improve its oral bioavailability. In this work, we evaluated the potential impact of NPs prepared from a grafted copolymer of polylactic acid and PEG on P-gp function by studying in vitro permeability of Famotidine across Caco-2 cells. Copolymers of PEG grafted on polylactic acid (PLA) backbone (PLA-g-PEG) were synthesised with 1mol% and 5mol% PEG vs. lactic acid monomer using PEG 750 and 2000Da. The polymers were used to prepare Famotidine-loaded NPs and tested in vitro on Caco-2 cells. Significant decrease in basolateral-to-apical transport of Famotidine was observed when Famotidine was encapsulated in NPs prepared from PLA-g-PEG5%. NPs prepared from PLA-g-PEG5% are promising to improve oral bioavailability of P-gp substrates.