Oral delivery remains the preferred route for chronic drug administration thanks to its patient convenience and compliance. However, many drug candidates are unsuitable for conventional oral formulations due to low solubility, poor membrane permeability, or extensive pre-systemic metabolism. This review describes a promising strategy that incorporates or encapsulates the molecules with biodegradable and biocompatible nanoparticulate carriers. The entrapped drug substances can be protected against degradation by gastrointestinal fluids, while drug absorption through the gastrointestinal epithelium or lymphatic transport can be enhanced. Possible mechanisms for transport of these nanocarriers across gastrointestinal mucosa are introduced that focus on effects of size and surface properties of the nanocarriers on the non-specific or targeted uptake by enterocytes and/or M cells. Applications of various oral nanocarrier formulations, such as lipid nanoparticles, nanoemulsions and chitosan nanoparticles, are reviewed. Nanoparticulate drug carriers show great potential for improving the bioavailability of orally administered drugs.