Low molecular weight heparins (LMWHs) are the standards of anticoagulant for the prevention of deep vein thrombosis (DVT) in patients undergoing arthroplasty and abdominal surgery. However, LMWHs are so far only administered by parenteral route. Thus, they are usually replaced by oral warfarin for outpatient therapy. Since warfarin has a slow onset and high incidence of drug-drug interaction, there is a great need for the development of an oral LMWH formulation. LMWH (tinzaparin)-loaded nanoparticles prepared with a blend of a polyester and a polycationic polymethacrylate by the double emulsion method were administered orally in fasted rabbits. The plasma tinzaparin concentration was measured by a chromogenic anti-factor Xa assay. After oral administration of two doses of tinzaparin-loaded nanoparticles (200 and 600 anti-Xa U/kg), the oral absorption was observed between 4 and 10 or 12 h, with a delayed onset of action ranging from 3 to 4 h. Mean absolute bioavailabilities were 51% and 59% for the two tested doses. We now report that the encapsulation of tinzaparin into nanoparticles is likely to contribute to its oral efficacy with an anticoagulant effect prolonged up to 8 h.